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 $219.28   7.171%   $235.0046   $235.00   $235.00   $235.00  
  Purchase #2 $89.82   8.387%   $97.3532   $97.35   $97.35   $97.40  
  Purchase #3 $44.48   8.674%   $48.3382   $48.34   $48.35   $48.30  
  Purchase #4 $240.29   11.836%   $268.7307   $268.73   $268.75   $268.70  
  Purchase #5 $19.26   11.781%   $21.529   $21.53   $21.55   $21.50  
  Purchase #6 $176.72   10.591%   $195.4364   $195.44   $195.45   $195.40  
  Purchase #7 $133.98   12.321%   $150.4877   $150.49   $150.50   $150.50  
  7 purchase totals = $923.83       $1,016.8798   $1,016.88   $1,016.95   $1,016.80