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 $248.91   11.546%   $277.6491   $277.65   $277.65   $277.60  
  Purchase #2 $224.52   3.637%   $232.6858   $232.69   $232.70   $232.70  
  Purchase #3 $189.65   6.186%   $201.3817   $201.38   $201.40   $201.40  
  Purchase #4 $146.34   8.847%   $159.2867   $159.29   $159.30   $159.30  
  Purchase #5 $165.99   6.321%   $176.4822   $176.48   $176.50   $176.50  
  Purchase #6 $221.74   10.141%   $244.2267   $244.23   $244.25   $244.20  
  Purchase #7 $58.59   13.792%   $66.6707   $66.67   $66.65   $66.70  
  7 purchase totals = $1,255.74       $1,358.3829   $1,358.39   $1,358.45   $1,358.40