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 $222.33   11.848%   $248.6717   $248.67   $248.65   $248.70  
  Purchase #2 $148.29   11.471%   $165.3003   $165.30   $165.30   $165.30  
  Purchase #3 $219.26   5.258%   $230.7887   $230.79   $230.80   $230.80  
  Purchase #4 $30.93   6.417%   $32.9148   $32.91   $32.90   $32.90  
  Purchase #5 $204.39   8.712%   $222.1965   $222.20   $222.20   $222.20  
  Purchase #6 $245.28   10.170%   $270.225   $270.23   $270.25   $270.20  
  Purchase #7 $224.43   4.105%   $233.6429   $233.64   $233.65   $233.60  
  7 purchase totals = $1,294.91       $1,403.7399   $1,403.74   $1,403.75   $1,403.70