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 $205.39   6.447%   $218.6315   $218.63   $218.65   $218.60  
  Purchase #2 $50.96   10.639%   $56.3816   $56.38   $56.40   $56.40  
  Purchase #3 $129.36   6.225%   $137.4127   $137.41   $137.40   $137.40  
  Purchase #4 $62.57   6.677%   $66.7478   $66.75   $66.75   $66.70  
  Purchase #5 $216.82   12.671%   $244.2933   $244.29   $244.30   $244.30  
  Purchase #6 $57.43   9.657%   $62.976   $62.98   $63.00   $63.00  
  Purchase #7 $233.44   5.307%   $245.8287   $245.83   $245.85   $245.80  
  7 purchase totals = $955.97       $1,032.2716   $1,032.27   $1,032.35   $1,032.20