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 $43.29   12.632%   $48.7584   $48.76   $48.75   $48.80  
  Purchase #2 $119.61   11.127%   $132.919   $132.92   $132.90   $132.90  
  Purchase #3 $67.73   10.666%   $74.9541   $74.95   $74.95   $75.00  
  Purchase #4 $238.46   6.715%   $254.4726   $254.47   $254.45   $254.50  
  Purchase #5 $177.45   9.337%   $194.0185   $194.02   $194.00   $194.00  
  Purchase #6 $74.86   10.211%   $82.504   $82.50   $82.50   $82.50  
  Purchase #7 $157.62   9.829%   $173.1125   $173.11   $173.10   $173.10  
  7 purchase totals = $879.02       $960.7391   $960.73   $960.65   $960.80