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 $188.97   9.107%   $206.1795   $206.18   $206.20   $206.20  
  Purchase #2 $53.82   11.347%   $59.927   $59.93   $59.95   $59.90  
  Purchase #3 $179.36   12.108%   $201.0769   $201.08   $201.10   $201.10  
  Purchase #4 $178.47   10.136%   $196.5597   $196.56   $196.55   $196.60  
  Purchase #5 $75.49   8.500%   $81.9067   $81.91   $81.90   $81.90  
  Purchase #6 $114.29   6.145%   $121.3131   $121.31   $121.30   $121.30  
  Purchase #7 $218.32   8.380%   $236.6152   $236.62   $236.60   $236.60  
  7 purchase totals = $1,008.72       $1,103.5781   $1,103.59   $1,103.60   $1,103.60