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 $114.54   3.257%   $118.2706   $118.27   $118.25   $118.30  
  Purchase #2 $53.94   6.198%   $57.2832   $57.28   $57.30   $57.30  
  Purchase #3 $17.70   6.355%   $18.8248   $18.82   $18.80   $18.80  
  Purchase #4 $166.99   7.821%   $180.0503   $180.05   $180.05   $180.10  
  Purchase #5 $171.89   5.195%   $180.8197   $180.82   $180.80   $180.80  
  Purchase #6 $246.61   5.833%   $260.9948   $260.99   $261.00   $261.00  
  Purchase #7 $64.82   6.167%   $68.8174   $68.82   $68.80   $68.80  
  7 purchase totals = $836.49       $885.0608   $885.05   $885.00   $885.10