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 $62.81   4.123%   $65.3997   $65.40   $65.40   $65.40  
  Purchase #2 $197.46   6.431%   $210.1587   $210.16   $210.15   $210.20  
  Purchase #3 $244.47   3.637%   $253.3614   $253.36   $253.35   $253.40  
  Purchase #4 $103.75   11.106%   $115.2725   $115.27   $115.25   $115.30  
  Purchase #5 $66.98   11.471%   $74.6633   $74.66   $74.65   $74.70  
  Purchase #6 $17.95   3.289%   $18.5404   $18.54   $18.55   $18.50  
  Purchase #7 $203.66   12.664%   $229.4515   $229.45   $229.45   $229.50  
  7 purchase totals = $897.08       $966.8475   $966.84   $966.80   $967.00