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 $44.89   10.493%   $49.6003   $49.60   $49.60   $49.60  
  Purchase #2 $24.35   7.662%   $26.2157   $26.22   $26.20   $26.20  
  Purchase #3 $210.32   11.422%   $234.3428   $234.34   $234.35   $234.30  
  Purchase #4 $223.53   5.650%   $236.1594   $236.16   $236.15   $236.20  
  Purchase #5 $194.51   12.197%   $218.2344   $218.23   $218.25   $218.20  
  Purchase #6 $93.51   5.122%   $98.2996   $98.30   $98.30   $98.30  
  Purchase #7 $143.45   12.769%   $161.7671   $161.77   $161.75   $161.80  
  7 purchase totals = $934.56       $1,024.6193   $1,024.62   $1,024.60   $1,024.60