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 $243.34   4.277%   $253.7477   $253.75   $253.75   $253.70  
  Purchase #2 $107.75   5.479%   $113.6536   $113.65   $113.65   $113.70  
  Purchase #3 $197.90   5.403%   $208.5925   $208.59   $208.60   $208.60  
  Purchase #4 $70.53   7.861%   $76.0744   $76.07   $76.05   $76.10  
  Purchase #5 $223.81   5.654%   $236.4642   $236.46   $236.45   $236.50  
  Purchase #6 $246.46   11.590%   $275.0247   $275.02   $275.00   $275.00  
  Purchase #7 $173.30   10.841%   $192.0875   $192.09   $192.10   $192.10  
  7 purchase totals = $1,263.09       $1,355.6446   $1,355.63   $1,355.60   $1,355.70