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 $83.59   10.433%   $92.3109   $92.31   $92.30   $92.30  
  Purchase #2 $32.57   6.467%   $34.6763   $34.68   $34.70   $34.70  
  Purchase #3 $195.72   3.104%   $201.7951   $201.80   $201.80   $201.80  
  Purchase #4 $74.97   8.436%   $81.2945   $81.29   $81.30   $81.30  
  Purchase #5 $32.40   12.174%   $36.3444   $36.34   $36.35   $36.30  
  Purchase #6 $152.25   3.103%   $156.9743   $156.97   $156.95   $157.00  
  Purchase #7 $140.89   7.615%   $151.6188   $151.62   $151.60   $151.60  
  7 purchase totals = $712.39       $755.0143   $755.01   $755.00   $755.00