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 $109.79   8.430%   $119.0453   $119.05   $119.05   $119.00  
  Purchase #2 $59.35   8.511%   $64.4013   $64.40   $64.40   $64.40  
  Purchase #3 $178.94   8.376%   $193.928   $193.93   $193.95   $193.90  
  Purchase #4 $244.59   5.215%   $257.3454   $257.35   $257.35   $257.30  
  Purchase #5 $233.56   8.542%   $253.5107   $253.51   $253.50   $253.50  
  Purchase #6 $177.33   8.386%   $192.2009   $192.20   $192.20   $192.20  
  Purchase #7 $76.63   3.187%   $79.0722   $79.07   $79.05   $79.10  
  7 purchase totals = $1,080.19       $1,159.5038   $1,159.51   $1,159.50   $1,159.40