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 $119.39   11.588%   $133.2249   $133.22   $133.20   $133.20  
  Purchase #2 $239.57   5.835%   $253.5489   $253.55   $253.55   $253.50  
  Purchase #3 $205.56   4.282%   $214.3621   $214.36   $214.35   $214.40  
  Purchase #4 $5.63   10.161%   $6.2021   $6.20   $6.20   $6.20  
  Purchase #5 $247.29   11.339%   $275.3302   $275.33   $275.35   $275.30  
  Purchase #6 $198.99   3.490%   $205.9348   $205.93   $205.95   $205.90  
  Purchase #7 $225.50   13.202%   $255.2705   $255.27   $255.25   $255.30  
  7 purchase totals = $1,241.93       $1,343.8735   $1,343.86   $1,343.85   $1,343.80