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 $243.85   10.159%   $268.6227   $268.62   $268.60   $268.60  
  Purchase #2 $194.94   10.626%   $215.6543   $215.65   $215.65   $215.70  
  Purchase #3 $48.57   11.110%   $53.9661   $53.97   $53.95   $54.00  
  Purchase #4 $69.79   8.354%   $75.6203   $75.62   $75.60   $75.60  
  Purchase #5 $18.54   13.615%   $21.0642   $21.06   $21.05   $21.10  
  Purchase #6 $108.95   6.226%   $115.7332   $115.73   $115.75   $115.70  
  Purchase #7 $101.34   9.431%   $110.8974   $110.90   $110.90   $110.90  
  7 purchase totals = $785.98       $861.5582   $861.55   $861.50   $861.60