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 $132.54   12.221%   $148.7377   $148.74   $148.75   $148.70  
  Purchase #2 $56.74   11.642%   $63.3457   $63.35   $63.35   $63.30  
  Purchase #3 $69.26   9.188%   $75.6236   $75.62   $75.60   $75.60  
  Purchase #4 $63.39   6.391%   $67.4413   $67.44   $67.45   $67.40  
  Purchase #5 $112.68   4.511%   $117.763   $117.76   $117.75   $117.80  
  Purchase #6 $72.84   4.755%   $76.3035   $76.30   $76.30   $76.30  
  Purchase #7 $169.73   12.248%   $190.5185   $190.52   $190.50   $190.50  
  7 purchase totals = $677.18       $739.7333   $739.73   $739.70   $739.60