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 $208.67   7.825%   $224.9984   $225.00   $225.00   $225.00  
  Purchase #2 $242.63   11.596%   $270.7654   $270.77   $270.75   $270.80  
  Purchase #3 $230.31   11.577%   $256.973   $256.97   $256.95   $257.00  
  Purchase #4 $26.63   6.463%   $28.3511   $28.35   $28.35   $28.40  
  Purchase #5 $208.62   4.684%   $218.3918   $218.39   $218.40   $218.40  
  Purchase #6 $78.69   8.409%   $85.307   $85.31   $85.30   $85.30  
  Purchase #7 $170.88   12.346%   $191.9768   $191.98   $192.00   $192.00  
  7 purchase totals = $1,166.43       $1,276.7635   $1,276.77   $1,276.75   $1,276.90