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 $67.68   8.511%   $73.4402   $73.44   $73.45   $73.40  
  Purchase #2 $205.95   13.136%   $233.0036   $233.00   $233.00   $233.00  
  Purchase #3 $34.53   13.248%   $39.1045   $39.10   $39.10   $39.10  
  Purchase #4 $216.83   4.254%   $226.0539   $226.05   $226.05   $226.10  
  Purchase #5 $158.71   9.785%   $174.2398   $174.24   $174.25   $174.20  
  Purchase #6 $135.56   6.548%   $144.4365   $144.44   $144.45   $144.40  
  Purchase #7 $142.96   12.397%   $160.6828   $160.68   $160.70   $160.70  
  7 purchase totals = $962.22       $1,050.9613   $1,050.95   $1,051.00   $1,050.90