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 $215.25   6.708%   $229.689   $229.69   $229.70   $229.70  
  Purchase #2 $58.65   3.146%   $60.4951   $60.50   $60.50   $60.50  
  Purchase #3 $237.66   11.248%   $264.392   $264.39   $264.40   $264.40  
  Purchase #4 $69.65   9.550%   $76.3016   $76.30   $76.30   $76.30  
  Purchase #5 $246.37   11.547%   $274.8183   $274.82   $274.80   $274.80  
  Purchase #6 $229.43   13.869%   $261.2496   $261.25   $261.25   $261.20  
  Purchase #7 $83.65   10.657%   $92.5646   $92.56   $92.55   $92.60  
  7 purchase totals = $1,140.66       $1,259.5102   $1,259.51   $1,259.50   $1,259.50