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 $34.32   10.813%   $38.031   $38.03   $38.05   $38.00  
  Purchase #2 $41.36   11.485%   $46.1102   $46.11   $46.10   $46.10  
  Purchase #3 $189.52   3.213%   $195.6093   $195.61   $195.60   $195.60  
  Purchase #4 $166.70   9.564%   $182.6432   $182.64   $182.65   $182.60  
  Purchase #5 $211.42   4.667%   $221.287   $221.29   $221.30   $221.30  
  Purchase #6 $40.76   13.339%   $46.197   $46.20   $46.20   $46.20  
  Purchase #7 $56.64   13.189%   $64.1102   $64.11   $64.10   $64.10  
  7 purchase totals = $740.72       $793.9879   $793.99   $794.00   $793.90