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 $59.78   5.866%   $63.2867   $63.29   $63.30   $63.30  
  Purchase #2 $98.50   13.702%   $111.9965   $112.00   $112.00   $112.00  
  Purchase #3 $176.31   8.593%   $191.4603   $191.46   $191.45   $191.50  
  Purchase #4 $136.56   5.837%   $144.531   $144.53   $144.55   $144.50  
  Purchase #5 $72.39   9.276%   $79.1049   $79.10   $79.10   $79.10  
  Purchase #6 $154.36   13.541%   $175.2619   $175.26   $175.25   $175.30  
  Purchase #7 $35.89   8.698%   $39.0117   $39.01   $39.00   $39.00  
  7 purchase totals = $733.79       $804.6530   $804.65   $804.65   $804.70