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 $88.47   12.461%   $99.4942   $99.49   $99.50   $99.50  
  Purchase #2 $131.92   3.445%   $136.4646   $136.46   $136.45   $136.50  
  Purchase #3 $212.34   5.363%   $223.7278   $223.73   $223.75   $223.70  
  Purchase #4 $230.89   12.605%   $259.9937   $259.99   $260.00   $260.00  
  Purchase #5 $214.33   9.467%   $234.6206   $234.62   $234.60   $234.60  
  Purchase #6 $159.80   8.526%   $173.4245   $173.42   $173.40   $173.40  
  Purchase #7 $157.44   11.345%   $175.3016   $175.30   $175.30   $175.30  
  7 purchase totals = $1,195.19       $1,303.0270   $1,303.01   $1,303.00   $1,303.00