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 $58.60   4.605%   $61.2985   $61.30   $61.30   $61.30  
  Purchase #2 $230.64   7.741%   $248.4938   $248.49   $248.50   $248.50  
  Purchase #3 $195.46   5.533%   $206.2748   $206.27   $206.25   $206.30  
  Purchase #4 $36.81   10.485%   $40.6695   $40.67   $40.65   $40.70  
  Purchase #5 $157.47   6.516%   $167.7307   $167.73   $167.75   $167.70  
  Purchase #6 $47.76   12.848%   $53.8962   $53.90   $53.90   $53.90  
  Purchase #7 $226.40   7.206%   $242.7144   $242.71   $242.70   $242.70  
  7 purchase totals = $953.14       $1,021.0779   $1,021.07   $1,021.05   $1,021.10