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 $164.99   10.794%   $182.799   $182.80   $182.80   $182.80  
  Purchase #2 $186.89   6.777%   $199.5555   $199.56   $199.55   $199.60  
  Purchase #3 $99.91   12.300%   $112.1989   $112.20   $112.20   $112.20  
  Purchase #4 $230.73   7.549%   $248.1478   $248.15   $248.15   $248.10  
  Purchase #5 $26.37   13.682%   $29.9779   $29.98   $30.00   $30.00  
  Purchase #6 $234.38   11.144%   $260.4993   $260.50   $260.50   $260.50  
  Purchase #7 $14.30   5.676%   $15.1117   $15.11   $15.10   $15.10  
  7 purchase totals = $957.57       $1,048.2901   $1,048.30   $1,048.30   $1,048.30