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 $124.67   13.683%   $141.7286   $141.73   $141.75   $141.70  
  Purchase #2 $131.38   9.169%   $143.4262   $143.43   $143.45   $143.40  
  Purchase #3 $44.65   5.534%   $47.1209   $47.12   $47.10   $47.10  
  Purchase #4 $196.90   4.347%   $205.4592   $205.46   $205.45   $205.50  
  Purchase #5 $167.96   11.451%   $187.1931   $187.19   $187.20   $187.20  
  Purchase #6 $83.47   4.733%   $87.4206   $87.42   $87.40   $87.40  
  Purchase #7 $91.42   11.433%   $101.872   $101.87   $101.85   $101.90  
  7 purchase totals = $840.45       $914.2206   $914.22   $914.20   $914.20