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 $50.43   12.535%   $56.7514   $56.75   $56.75   $56.80  
  Purchase #2 $189.45   11.605%   $211.4357   $211.44   $211.45   $211.40  
  Purchase #3 $155.35   12.793%   $175.2239   $175.22   $175.20   $175.20  
  Purchase #4 $98.76   7.220%   $105.8905   $105.89   $105.90   $105.90  
  Purchase #5 $244.63   6.375%   $260.2252   $260.23   $260.25   $260.20  
  Purchase #6 $91.89   12.263%   $103.1585   $103.16   $103.15   $103.20  
  Purchase #7 $44.37   5.784%   $46.9364   $46.94   $46.95   $46.90  
  7 purchase totals = $874.88       $959.6216   $959.63   $959.65   $959.60