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 $201.93   11.735%   $225.6265   $225.63   $225.65   $225.60  
  Purchase #2 $33.65   11.817%   $37.6264   $37.63   $37.65   $37.60  
  Purchase #3 $62.99   13.182%   $71.2933   $71.29   $71.30   $71.30  
  Purchase #4 $16.32   11.283%   $18.1614   $18.16   $18.15   $18.20  
  Purchase #5 $217.41   4.176%   $226.489   $226.49   $226.50   $226.50  
  Purchase #6 $234.97   6.218%   $249.5804   $249.58   $249.60   $249.60  
  Purchase #7 $68.98   5.351%   $72.6711   $72.67   $72.65   $72.70  
  7 purchase totals = $836.25       $901.4481   $901.45   $901.50   $901.50