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 $58.97   13.211%   $66.7605   $66.76   $66.75   $66.80  
  Purchase #2 $177.81   12.102%   $199.3286   $199.33   $199.35   $199.30  
  Purchase #3 $55.69   8.492%   $60.4192   $60.42   $60.40   $60.40  
  Purchase #4 $240.63   8.283%   $260.5614   $260.56   $260.55   $260.60  
  Purchase #5 $185.39   7.405%   $199.1181   $199.12   $199.10   $199.10  
  Purchase #6 $127.60   3.711%   $132.3352   $132.34   $132.35   $132.30  
  Purchase #7 $132.25   13.749%   $150.4331   $150.43   $150.45   $150.40  
  7 purchase totals = $978.34       $1,068.9561   $1,068.96   $1,068.95   $1,068.90