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 $151.46   11.268%   $168.5265   $168.53   $168.55   $168.50  
  Purchase #2 $95.78   7.301%   $102.7729   $102.77   $102.75   $102.80  
  Purchase #3 $127.88   6.436%   $136.1104   $136.11   $136.10   $136.10  
  Purchase #4 $203.89   6.635%   $217.4181   $217.42   $217.40   $217.40  
  Purchase #5 $88.38   5.782%   $93.4901   $93.49   $93.50   $93.50  
  Purchase #6 $123.93   6.431%   $131.8999   $131.90   $131.90   $131.90  
  Purchase #7 $42.42   5.506%   $44.7556   $44.76   $44.75   $44.80  
  7 purchase totals = $833.74       $894.9735   $894.98   $894.95   $895.00