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 $29.28   9.338%   $32.0142   $32.01   $32.00   $32.00  
  Purchase #2 $152.27   9.178%   $166.2453   $166.25   $166.25   $166.20  
  Purchase #3 $78.66   11.612%   $87.794   $87.79   $87.80   $87.80  
  Purchase #4 $24.48   12.472%   $27.5331   $27.53   $27.55   $27.50  
  Purchase #5 $176.78   11.574%   $197.2405   $197.24   $197.25   $197.20  
  Purchase #6 $45.79   6.853%   $48.928   $48.93   $48.95   $48.90  
  Purchase #7 $50.83   6.503%   $54.1355   $54.14   $54.15   $54.10  
  7 purchase totals = $558.09       $613.8906   $613.89   $613.95   $613.70