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 $250.34   7.453%   $268.9978   $269.00   $269.00   $269.00  
  Purchase #2 $59.62   4.571%   $62.3452   $62.35   $62.35   $62.30  
  Purchase #3 $27.46   11.762%   $30.6898   $30.69   $30.70   $30.70  
  Purchase #4 $54.25   11.706%   $60.6005   $60.60   $60.60   $60.60  
  Purchase #5 $245.95   9.359%   $268.9685   $268.97   $268.95   $269.00  
  Purchase #6 $229.69   4.140%   $239.1992   $239.20   $239.20   $239.20  
  Purchase #7 $179.30   3.450%   $185.4859   $185.49   $185.50   $185.50  
  7 purchase totals = $1,046.61       $1,116.2869   $1,116.30   $1,116.30   $1,116.30