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 $235.34   5.362%   $247.9589   $247.96   $247.95   $248.00  
  Purchase #2 $217.25   4.832%   $227.7475   $227.75   $227.75   $227.70  
  Purchase #3 $123.95   6.799%   $132.3774   $132.38   $132.40   $132.40  
  Purchase #4 $91.43   5.576%   $96.5281   $96.53   $96.55   $96.50  
  Purchase #5 $97.82   11.599%   $109.1661   $109.17   $109.15   $109.20  
  Purchase #6 $69.45   11.448%   $77.4006   $77.40   $77.40   $77.40  
  Purchase #7 $136.96   11.738%   $153.0364   $153.04   $153.05   $153.00  
  7 purchase totals = $972.20       $1,044.2150   $1,044.23   $1,044.25   $1,044.20