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 $186.99   10.329%   $206.3042   $206.30   $206.30   $206.30  
  Purchase #2 $63.27   12.574%   $71.2256   $71.23   $71.25   $71.20  
  Purchase #3 $223.39   4.253%   $232.8908   $232.89   $232.90   $232.90  
  Purchase #4 $126.29   5.144%   $132.7864   $132.79   $132.80   $132.80  
  Purchase #5 $141.91   4.105%   $147.7354   $147.74   $147.75   $147.70  
  Purchase #6 $249.92   5.668%   $264.0855   $264.09   $264.10   $264.10  
  Purchase #7 $45.30   13.237%   $51.2964   $51.30   $51.30   $51.30  
  7 purchase totals = $1,037.07       $1,106.3243   $1,106.34   $1,106.40   $1,106.30