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 $34.51   11.444%   $38.4593   $38.46   $38.45   $38.50  
  Purchase #2 $112.86   5.479%   $119.0436   $119.04   $119.05   $119.00  
  Purchase #3 $204.76   9.555%   $224.3248   $224.32   $224.30   $224.30  
  Purchase #4 $85.85   11.353%   $95.5966   $95.60   $95.60   $95.60  
  Purchase #5 $220.74   3.128%   $227.6447   $227.64   $227.65   $227.60  
  Purchase #6 $143.38   6.277%   $152.38   $152.38   $152.40   $152.40  
  Purchase #7 $62.53   11.274%   $69.5796   $69.58   $69.60   $69.60  
  7 purchase totals = $864.63       $927.0286   $927.02   $927.05   $927.00