Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $193.73   4.276%   $202.0139   $202.01   $202.00   $202.00  
  Purchase #2 $239.63   11.470%   $267.1156   $267.12   $267.10   $267.10  
  Purchase #3 $145.37   11.418%   $161.9683   $161.97   $161.95   $162.00  
  Purchase #4 $154.78   12.624%   $174.3194   $174.32   $174.30   $174.30  
  Purchase #5 $229.65   9.361%   $251.1475   $251.15   $251.15   $251.10  
  Purchase #6 $220.40   8.474%   $239.0767   $239.08   $239.10   $239.10  
  Purchase #7 $101.93   12.229%   $114.395   $114.40   $114.40   $114.40  
  7 purchase totals = $1,285.49       $1,410.0364   $1,410.05   $1,410.00   $1,410.00