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 $205.68   13.385%   $233.2103   $233.21   $233.20   $233.20  
  Purchase #2 $101.72   4.746%   $106.5476   $106.55   $106.55   $106.50  
  Purchase #3 $50.44   3.584%   $52.2478   $52.25   $52.25   $52.20  
  Purchase #4 $242.83   6.446%   $258.4828   $258.48   $258.50   $258.50  
  Purchase #5 $112.93   5.142%   $118.7369   $118.74   $118.75   $118.70  
  Purchase #6 $17.75   12.110%   $19.8995   $19.90   $19.90   $19.90  
  Purchase #7 $83.79   9.851%   $92.0442   $92.04   $92.05   $92.00  
  7 purchase totals = $815.14       $881.1691   $881.17   $881.20   $881.00