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 $240.87   11.613%   $268.8422   $268.84   $268.85   $268.80  
  Purchase #2 $49.27   13.741%   $56.0402   $56.04   $56.05   $56.00  
  Purchase #3 $215.77   10.601%   $238.6438   $238.64   $238.65   $238.60  
  Purchase #4 $21.63   10.478%   $23.8964   $23.90   $23.90   $23.90  
  Purchase #5 $165.51   11.381%   $184.3467   $184.35   $184.35   $184.30  
  Purchase #6 $106.78   5.123%   $112.2503   $112.25   $112.25   $112.30  
  Purchase #7 $63.87   6.190%   $67.8236   $67.82   $67.80   $67.80  
  7 purchase totals = $863.70       $951.8432   $951.84   $951.85   $951.70