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 $88.34   9.733%   $96.9381   $96.94   $96.95   $96.90  
  Purchase #2 $99.65   4.776%   $104.4093   $104.41   $104.40   $104.40  
  Purchase #3 $53.79   12.378%   $60.4481   $60.45   $60.45   $60.40  
  Purchase #4 $249.52   6.714%   $266.2728   $266.27   $266.25   $266.30  
  Purchase #5 $19.77   6.560%   $21.0669   $21.07   $21.05   $21.10  
  Purchase #6 $152.82   11.192%   $169.9236   $169.92   $169.90   $169.90  
  Purchase #7 $239.83   4.291%   $250.1211   $250.12   $250.10   $250.10  
  7 purchase totals = $903.72       $969.1799   $969.18   $969.10   $969.10