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 $46.95   13.257%   $53.1742   $53.17   $53.15   $53.20  
  Purchase #2 $55.96   13.176%   $63.3333   $63.33   $63.35   $63.30  
  Purchase #3 $91.26   11.515%   $101.7686   $101.77   $101.75   $101.80  
  Purchase #4 $208.75   3.599%   $216.2629   $216.26   $216.25   $216.30  
  Purchase #5 $12.56   11.423%   $13.9947   $13.99   $14.00   $14.00  
  Purchase #6 $153.60   9.299%   $167.8833   $167.88   $167.90   $167.90  
  Purchase #7 $188.90   3.351%   $195.23   $195.23   $195.25   $195.20  
  7 purchase totals = $757.98       $811.6470   $811.63   $811.65   $811.70