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 $67.38   12.350%   $75.7014   $75.70   $75.70   $75.70  
  Purchase #2 $239.29   11.495%   $266.7964   $266.80   $266.80   $266.80  
  Purchase #3 $162.71   4.432%   $169.9213   $169.92   $169.90   $169.90  
  Purchase #4 $174.31   4.708%   $182.5165   $182.52   $182.50   $182.50  
  Purchase #5 $62.92   9.368%   $68.8143   $68.81   $68.80   $68.80  
  Purchase #6 $139.44   8.574%   $151.3956   $151.40   $151.40   $151.40  
  Purchase #7 $96.33   4.588%   $100.7496   $100.75   $100.75   $100.70  
  7 purchase totals = $942.38       $1,015.8951   $1,015.90   $1,015.85   $1,015.80