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 $49.59   13.426%   $56.248   $56.25   $56.25   $56.20  
  Purchase #2 $229.71   12.468%   $258.3502   $258.35   $258.35   $258.40  
  Purchase #3 $155.31   11.480%   $173.1396   $173.14   $173.15   $173.10  
  Purchase #4 $73.92   4.842%   $77.4992   $77.50   $77.50   $77.50  
  Purchase #5 $16.84   8.532%   $18.2768   $18.28   $18.30   $18.30  
  Purchase #6 $194.39   9.773%   $213.3877   $213.39   $213.40   $213.40  
  Purchase #7 $24.96   3.149%   $25.746   $25.75   $25.75   $25.70  
  7 purchase totals = $744.72       $822.6475   $822.66   $822.70   $822.60