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 $111.99   6.493%   $119.2615   $119.26   $119.25   $119.30  
  Purchase #2 $57.63   13.547%   $65.4371   $65.44   $65.45   $65.40  
  Purchase #3 $110.78   5.417%   $116.781   $116.78   $116.80   $116.80  
  Purchase #4 $249.68   8.680%   $271.3522   $271.35   $271.35   $271.40  
  Purchase #5 $226.29   5.104%   $237.8398   $237.84   $237.85   $237.80  
  Purchase #6 $27.62   10.471%   $30.5121   $30.51   $30.50   $30.50  
  Purchase #7 $161.99   8.555%   $175.8482   $175.85   $175.85   $175.80  
  7 purchase totals = $945.98       $1,017.0319   $1,017.03   $1,017.05   $1,017.00