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 $194.43   12.819%   $219.354   $219.35   $219.35   $219.40  
  Purchase #2 $249.34   9.313%   $272.561   $272.56   $272.55   $272.60  
  Purchase #3 $225.62   10.692%   $249.7433   $249.74   $249.75   $249.70  
  Purchase #4 $68.62   4.553%   $71.7443   $71.74   $71.75   $71.70  
  Purchase #5 $98.75   4.763%   $103.4535   $103.45   $103.45   $103.50  
  Purchase #6 $69.31   10.500%   $76.5876   $76.59   $76.60   $76.60  
  Purchase #7 $14.66   10.383%   $16.1821   $16.18   $16.20   $16.20  
  7 purchase totals = $920.73       $1,009.6258   $1,009.61   $1,009.65   $1,009.70