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 $62.92   12.787%   $70.9656   $70.97   $70.95   $71.00  
  Purchase #2 $127.95   12.568%   $144.0308   $144.03   $144.05   $144.00  
  Purchase #3 $67.85   11.642%   $75.7491   $75.75   $75.75   $75.70  
  Purchase #4 $113.38   5.804%   $119.9606   $119.96   $119.95   $120.00  
  Purchase #5 $210.88   10.311%   $232.6238   $232.62   $232.60   $232.60  
  Purchase #6 $67.66   12.376%   $76.0336   $76.03   $76.05   $76.00  
  Purchase #7 $236.87   13.364%   $268.5253   $268.53   $268.55   $268.50  
  7 purchase totals = $887.51       $987.8888   $987.89   $987.90   $987.80