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 $247.61   6.219%   $263.0089   $263.01   $263.00   $263.00  
  Purchase #2 $44.35   5.439%   $46.7622   $46.76   $46.75   $46.80  
  Purchase #3 $82.71   11.361%   $92.1067   $92.11   $92.10   $92.10  
  Purchase #4 $233.45   5.183%   $245.5497   $245.55   $245.55   $245.50  
  Purchase #5 $222.62   10.190%   $245.305   $245.31   $245.30   $245.30  
  Purchase #6 $89.73   3.750%   $93.0949   $93.09   $93.10   $93.10  
  Purchase #7 $225.72   6.791%   $241.0486   $241.05   $241.05   $241.00  
  7 purchase totals = $1,146.19       $1,226.8760   $1,226.88   $1,226.85   $1,226.80