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 $54.94   9.532%   $60.1769   $60.18   $60.20   $60.20  
  Purchase #2 $230.35   12.339%   $258.7729   $258.77   $258.75   $258.80  
  Purchase #3 $169.54   10.638%   $187.5757   $187.58   $187.60   $187.60  
  Purchase #4 $129.43   4.367%   $135.0822   $135.08   $135.10   $135.10  
  Purchase #5 $85.67   10.717%   $94.8513   $94.85   $94.85   $94.90  
  Purchase #6 $89.61   5.346%   $94.4006   $94.40   $94.40   $94.40  
  Purchase #7 $125.34   9.224%   $136.9014   $136.90   $136.90   $136.90  
  7 purchase totals = $884.88       $967.7610   $967.76   $967.80   $967.90