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 $186.68   4.455%   $194.9966   $195.00   $195.00   $195.00  
  Purchase #2 $94.36   12.444%   $106.1022   $106.10   $106.10   $106.10  
  Purchase #3 $214.53   5.523%   $226.3785   $226.38   $226.40   $226.40  
  Purchase #4 $79.95   9.423%   $87.4837   $87.48   $87.50   $87.50  
  Purchase #5 $83.65   13.438%   $94.8909   $94.89   $94.90   $94.90  
  Purchase #6 $230.65   10.156%   $254.0748   $254.07   $254.05   $254.10  
  Purchase #7 $237.63   11.538%   $265.0477   $265.05   $265.05   $265.00  
  7 purchase totals = $1,127.45       $1,228.9744   $1,228.97   $1,229.00   $1,229.00