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 $114.89   6.798%   $122.7002   $122.70   $122.70   $122.70  
  Purchase #2 $54.44   11.343%   $60.6151   $60.62   $60.60   $60.60  
  Purchase #3 $108.34   8.463%   $117.5088   $117.51   $117.50   $117.50  
  Purchase #4 $133.34   3.778%   $138.3776   $138.38   $138.40   $138.40  
  Purchase #5 $91.73   6.164%   $97.3842   $97.38   $97.40   $97.40  
  Purchase #6 $59.76   3.323%   $61.7458   $61.75   $61.75   $61.70  
  Purchase #7 $242.51   13.691%   $275.712   $275.71   $275.70   $275.70  
  7 purchase totals = $805.01       $874.0437   $874.05   $874.05   $874.00