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 $217.47   12.762%   $245.2235   $245.22   $245.20   $245.20  
  Purchase #2 $93.53   12.185%   $104.9266   $104.93   $104.95   $104.90  
  Purchase #3 $195.97   12.657%   $220.7739   $220.77   $220.75   $220.80  
  Purchase #4 $91.42   5.706%   $96.6364   $96.64   $96.65   $96.60  
  Purchase #5 $154.59   11.321%   $172.0911   $172.09   $172.10   $172.10  
  Purchase #6 $80.93   4.607%   $84.6584   $84.66   $84.65   $84.70  
  Purchase #7 $215.33   11.324%   $239.714   $239.71   $239.70   $239.70  
  7 purchase totals = $1,049.24       $1,164.0239   $1,164.02   $1,164.00   $1,164.00