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 $237.51   12.568%   $267.3603   $267.36   $267.35   $267.40  
  Purchase #2 $35.44   5.800%   $37.4955   $37.50   $37.50   $37.50  
  Purchase #3 $162.79   5.422%   $171.6165   $171.62   $171.60   $171.60  
  Purchase #4 $76.75   11.696%   $85.7267   $85.73   $85.75   $85.70  
  Purchase #5 $109.67   8.132%   $118.5884   $118.59   $118.60   $118.60  
  Purchase #6 $93.80   9.407%   $102.6238   $102.62   $102.60   $102.60  
  Purchase #7 $157.91   3.106%   $162.8147   $162.81   $162.80   $162.80  
  7 purchase totals = $873.87       $946.2259   $946.23   $946.20   $946.20