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 $200.34   10.644%   $221.6642   $221.66   $221.65   $221.70  
  Purchase #2 $209.55   7.358%   $224.9687   $224.97   $224.95   $225.00  
  Purchase #3 $87.25   11.513%   $97.2951   $97.30   $97.30   $97.30  
  Purchase #4 $165.62   11.446%   $184.5769   $184.58   $184.60   $184.60  
  Purchase #5 $6.32   7.322%   $6.7828   $6.78   $6.80   $6.80  
  Purchase #6 $167.63   10.629%   $185.4474   $185.45   $185.45   $185.40  
  Purchase #7 $46.52   3.622%   $48.205   $48.21   $48.20   $48.20  
  7 purchase totals = $883.23       $968.9401   $968.95   $968.95   $969.00