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 $216.88   3.556%   $224.5923   $224.59   $224.60   $224.60  
  Purchase #2 $53.31   9.643%   $58.4507   $58.45   $58.45   $58.50  
  Purchase #3 $68.57   12.816%   $77.3579   $77.36   $77.35   $77.40  
  Purchase #4 $18.43   11.342%   $20.5203   $20.52   $20.50   $20.50  
  Purchase #5 $116.78   11.311%   $129.989   $129.99   $130.00   $130.00  
  Purchase #6 $107.56   8.389%   $116.5832   $116.58   $116.60   $116.60  
  Purchase #7 $213.96   12.534%   $240.7777   $240.78   $240.80   $240.80  
  7 purchase totals = $795.49       $868.2711   $868.27   $868.30   $868.40