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 $131.94   12.744%   $148.7544   $148.75   $148.75   $148.80  
  Purchase #2 $240.50   10.318%   $265.3148   $265.31   $265.30   $265.30  
  Purchase #3 $73.38   12.307%   $82.4109   $82.41   $82.40   $82.40  
  Purchase #4 $188.41   13.164%   $213.2123   $213.21   $213.20   $213.20  
  Purchase #5 $249.68   4.306%   $260.4312   $260.43   $260.45   $260.40  
  Purchase #6 $117.78   8.157%   $127.3873   $127.39   $127.40   $127.40  
  Purchase #7 $101.86   4.221%   $106.1595   $106.16   $106.15   $106.20  
  7 purchase totals = $1,103.55       $1,203.6704   $1,203.66   $1,203.65   $1,203.70