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 $249.67   5.591%   $263.629   $263.63   $263.65   $263.60  
  Purchase #2 $235.55   3.309%   $243.3443   $243.34   $243.35   $243.30  
  Purchase #3 $223.76   10.725%   $247.7583   $247.76   $247.75   $247.80  
  Purchase #4 $88.58   4.708%   $92.7503   $92.75   $92.75   $92.80  
  Purchase #5 $213.32   7.680%   $229.703   $229.70   $229.70   $229.70  
  Purchase #6 $237.91   8.856%   $258.9793   $258.98   $259.00   $259.00  
  Purchase #7 $15.45   6.567%   $16.4646   $16.46   $16.45   $16.50  
  7 purchase totals = $1,264.24       $1,352.6288   $1,352.62   $1,352.65   $1,352.70