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 $111.87   9.505%   $122.5032   $122.50   $122.50   $122.50  
  Purchase #2 $219.29   6.676%   $233.9298   $233.93   $233.95   $233.90  
  Purchase #3 $157.47   5.662%   $166.386   $166.39   $166.40   $166.40  
  Purchase #4 $79.51   4.793%   $83.3209   $83.32   $83.30   $83.30  
  Purchase #5 $48.95   4.807%   $51.303   $51.30   $51.30   $51.30  
  Purchase #6 $202.90   7.395%   $217.9045   $217.90   $217.90   $217.90  
  Purchase #7 $132.90   9.848%   $145.988   $145.99   $146.00   $146.00  
  7 purchase totals = $952.89       $1,021.3354   $1,021.33   $1,021.35   $1,021.30