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 $244.69   4.712%   $256.2198   $256.22   $256.20   $256.20  
  Purchase #2 $121.90   12.134%   $136.6913   $136.69   $136.70   $136.70  
  Purchase #3 $46.75   13.583%   $53.1001   $53.10   $53.10   $53.10  
  Purchase #4 $218.77   5.277%   $230.3145   $230.31   $230.30   $230.30  
  Purchase #5 $94.45   3.743%   $97.9853   $97.99   $98.00   $98.00  
  Purchase #6 $238.43   10.652%   $263.8276   $263.83   $263.85   $263.80  
  Purchase #7 $81.74   3.181%   $84.3401   $84.34   $84.35   $84.30  
  7 purchase totals = $1,046.73       $1,122.4787   $1,122.48   $1,122.50   $1,122.40