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 $146.54   4.227%   $152.7342   $152.73   $152.75   $152.70  
  Purchase #2 $181.41   13.106%   $205.1856   $205.19   $205.20   $205.20  
  Purchase #3 $132.47   3.238%   $136.7594   $136.76   $136.75   $136.80  
  Purchase #4 $199.62   9.241%   $218.0669   $218.07   $218.05   $218.10  
  Purchase #5 $47.79   11.159%   $53.1229   $53.12   $53.10   $53.10  
  Purchase #6 $45.57   5.166%   $47.9241   $47.92   $47.90   $47.90  
  Purchase #7 $228.66   12.675%   $257.6427   $257.64   $257.65   $257.60  
  7 purchase totals = $982.06       $1,071.4358   $1,071.43   $1,071.40   $1,071.40