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 $55.97   13.420%   $63.4812   $63.48   $63.50   $63.50  
  Purchase #2 $108.84   7.739%   $117.2631   $117.26   $117.25   $117.30  
  Purchase #3 $118.53   6.148%   $125.8172   $125.82   $125.80   $125.80  
  Purchase #4 $133.94   9.641%   $146.8532   $146.85   $146.85   $146.90  
  Purchase #5 $97.93   3.358%   $101.2185   $101.22   $101.20   $101.20  
  Purchase #6 $180.61   6.737%   $192.7777   $192.78   $192.80   $192.80  
  Purchase #7 $240.82   10.578%   $266.2939   $266.29   $266.30   $266.30  
  7 purchase totals = $936.64       $1,013.7048   $1,013.70   $1,013.70   $1,013.80