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 $63.99   4.208%   $66.6827   $66.68   $66.70   $66.70  
  Purchase #2 $91.69   11.749%   $102.4627   $102.46   $102.45   $102.50  
  Purchase #3 $58.64   6.698%   $62.5677   $62.57   $62.55   $62.60  
  Purchase #4 $124.66   6.387%   $132.622   $132.62   $132.60   $132.60  
  Purchase #5 $48.52   13.694%   $55.1643   $55.16   $55.15   $55.20  
  Purchase #6 $244.36   9.365%   $267.2443   $267.24   $267.25   $267.20  
  Purchase #7 $64.79   5.404%   $68.2913   $68.29   $68.30   $68.30  
  7 purchase totals = $696.65       $755.0350   $755.02   $755.00   $755.10