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 $48.63   7.161%   $52.1124   $52.11   $52.10   $52.10  
  Purchase #2 $114.47   7.419%   $122.9625   $122.96   $122.95   $123.00  
  Purchase #3 $219.92   4.166%   $229.0819   $229.08   $229.10   $229.10  
  Purchase #4 $234.81   11.211%   $261.1345   $261.13   $261.15   $261.10  
  Purchase #5 $53.34   13.533%   $60.5585   $60.56   $60.55   $60.60  
  Purchase #6 $159.40   8.372%   $172.745   $172.75   $172.75   $172.70  
  Purchase #7 $49.68   3.109%   $51.2246   $51.22   $51.20   $51.20  
  7 purchase totals = $880.25       $949.8194   $949.81   $949.80   $949.80