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 $224.41   3.864%   $233.0812   $233.08   $233.10   $233.10  
  Purchase #2 $245.57   8.327%   $266.0186   $266.02   $266.00   $266.00  
  Purchase #3 $101.88   12.185%   $114.2941   $114.29   $114.30   $114.30  
  Purchase #4 $178.36   3.346%   $184.3279   $184.33   $184.35   $184.30  
  Purchase #5 $130.45   7.302%   $139.9755   $139.98   $140.00   $140.00  
  Purchase #6 $96.32   9.503%   $105.4733   $105.47   $105.45   $105.50  
  Purchase #7 $194.86   4.557%   $203.7398   $203.74   $203.75   $203.70  
  7 purchase totals = $1,171.85       $1,246.9104   $1,246.91   $1,246.95   $1,246.90