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 $68.34   12.546%   $76.9139   $76.91   $76.90   $76.90  
  Purchase #2 $244.47   3.646%   $253.3834   $253.38   $253.40   $253.40  
  Purchase #3 $119.59   3.528%   $123.8091   $123.81   $123.80   $123.80  
  Purchase #4 $178.28   5.527%   $188.1335   $188.13   $188.15   $188.10  
  Purchase #5 $62.51   11.521%   $69.7118   $69.71   $69.70   $69.70  
  Purchase #6 $225.49   3.263%   $232.8477   $232.85   $232.85   $232.80  
  Purchase #7 $135.55   9.695%   $148.6916   $148.69   $148.70   $148.70  
  7 purchase totals = $1,034.23       $1,093.4910   $1,093.48   $1,093.50   $1,093.40