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 $90.71   5.866%   $96.031   $96.03   $96.05   $96.00  
  Purchase #2 $250.59   8.188%   $271.1083   $271.11   $271.10   $271.10  
  Purchase #3 $241.65   5.822%   $255.7189   $255.72   $255.70   $255.70  
  Purchase #4 $209.98   13.829%   $239.0181   $239.02   $239.00   $239.00  
  Purchase #5 $29.27   5.312%   $30.8248   $30.82   $30.80   $30.80  
  Purchase #6 $161.77   13.244%   $183.1948   $183.19   $183.20   $183.20  
  Purchase #7 $65.69   7.308%   $70.4906   $70.49   $70.50   $70.50  
  7 purchase totals = $1,049.66       $1,146.3865   $1,146.38   $1,146.35   $1,146.30