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 $117.95   5.143%   $124.0162   $124.02   $124.00   $124.00  
  Purchase #2 $58.73   11.179%   $65.2954   $65.30   $65.30   $65.30  
  Purchase #3 $77.66   10.487%   $85.8042   $85.80   $85.80   $85.80  
  Purchase #4 $203.48   3.566%   $210.7361   $210.74   $210.75   $210.70  
  Purchase #5 $152.34   11.335%   $169.6077   $169.61   $169.60   $169.60  
  Purchase #6 $158.89   10.348%   $175.3319   $175.33   $175.35   $175.30  
  Purchase #7 $18.50   12.189%   $20.755   $20.76   $20.75   $20.80  
  7 purchase totals = $787.55       $851.5465   $851.56   $851.55   $851.50