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 $50.44   11.527%   $56.2542   $56.25   $56.25   $56.30  
  Purchase #2 $169.80   7.805%   $183.0529   $183.05   $183.05   $183.10  
  Purchase #3 $51.43   10.865%   $57.0179   $57.02   $57.00   $57.00  
  Purchase #4 $29.44   9.511%   $32.24   $32.24   $32.25   $32.20  
  Purchase #5 $249.86   11.780%   $279.2935   $279.29   $279.30   $279.30  
  Purchase #6 $148.31   6.303%   $157.658   $157.66   $157.65   $157.70  
  Purchase #7 $159.92   8.120%   $172.9055   $172.91   $172.90   $172.90  
  7 purchase totals = $859.20       $938.4220   $938.42   $938.40   $938.50