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 $96.29   5.479%   $101.5657   $101.57   $101.55   $101.60  
  Purchase #2 $90.87   3.410%   $93.9687   $93.97   $93.95   $94.00  
  Purchase #3 $27.93   13.426%   $31.6799   $31.68   $31.70   $31.70  
  Purchase #4 $36.36   13.308%   $41.1988   $41.20   $41.20   $41.20  
  Purchase #5 $91.99   4.725%   $96.3365   $96.34   $96.35   $96.30  
  Purchase #6 $69.66   6.291%   $74.0423   $74.04   $74.05   $74.00  
  Purchase #7 $42.36   12.392%   $47.6093   $47.61   $47.60   $47.60  
  7 purchase totals = $455.46       $486.4012   $486.41   $486.40   $486.40