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 $84.84   10.271%   $93.5539   $93.55   $93.55   $93.60  
  Purchase #2 $231.34   9.461%   $253.2271   $253.23   $253.25   $253.20  
  Purchase #3 $195.35   6.257%   $207.573   $207.57   $207.55   $207.60  
  Purchase #4 $108.43   3.831%   $112.584   $112.58   $112.60   $112.60  
  Purchase #5 $154.65   5.730%   $163.5114   $163.51   $163.50   $163.50  
  Purchase #6 $119.53   3.457%   $123.6622   $123.66   $123.65   $123.70  
  Purchase #7 $19.46   8.215%   $21.0586   $21.06   $21.05   $21.10  
  7 purchase totals = $913.60       $975.1702   $975.16   $975.15   $975.30