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 $65.44   5.355%   $68.9443   $68.94   $68.95   $68.90  
  Purchase #2 $90.58   3.410%   $93.6688   $93.67   $93.65   $93.70  
  Purchase #3 $213.96   5.665%   $226.0808   $226.08   $226.10   $226.10  
  Purchase #4 $151.53   7.187%   $162.4205   $162.42   $162.40   $162.40  
  Purchase #5 $214.58   11.178%   $238.5658   $238.57   $238.55   $238.60  
  Purchase #6 $44.99   8.717%   $48.9118   $48.91   $48.90   $48.90  
  Purchase #7 $102.38   10.213%   $112.8361   $112.84   $112.85   $112.80  
  7 purchase totals = $883.46       $951.4281   $951.43   $951.40   $951.40