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 $201.62   10.363%   $222.5139   $222.51   $222.50   $222.50  
  Purchase #2 $44.68   8.180%   $48.3348   $48.33   $48.35   $48.30  
  Purchase #3 $99.26   8.420%   $107.6177   $107.62   $107.60   $107.60  
  Purchase #4 $92.87   11.186%   $103.2584   $103.26   $103.25   $103.30  
  Purchase #5 $44.54   8.672%   $48.4025   $48.40   $48.40   $48.40  
  Purchase #6 $216.52   9.604%   $237.3146   $237.31   $237.30   $237.30  
  Purchase #7 $101.81   5.643%   $107.5551   $107.56   $107.55   $107.60  
  7 purchase totals = $801.30       $874.9970   $874.99   $874.95   $875.00