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 $248.53   5.834%   $263.0292   $263.03   $263.05   $263.00  
  Purchase #2 $246.90   6.129%   $262.0325   $262.03   $262.05   $262.00  
  Purchase #3 $88.37   4.235%   $92.1125   $92.11   $92.10   $92.10  
  Purchase #4 $117.83   12.737%   $132.838   $132.84   $132.85   $132.80  
  Purchase #5 $205.39   13.566%   $233.2532   $233.25   $233.25   $233.30  
  Purchase #6 $236.30   8.168%   $255.601   $255.60   $255.60   $255.60  
  Purchase #7 $149.36   5.432%   $157.4732   $157.47   $157.45   $157.50  
  7 purchase totals = $1,292.68       $1,396.3396   $1,396.33   $1,396.35   $1,396.30