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 $53.78   13.364%   $60.9672   $60.97   $60.95   $61.00  
  Purchase #2 $52.93   3.345%   $54.7005   $54.70   $54.70   $54.70  
  Purchase #3 $206.90   11.702%   $231.1114   $231.11   $231.10   $231.10  
  Purchase #4 $112.60   10.428%   $124.3419   $124.34   $124.35   $124.30  
  Purchase #5 $196.38   9.346%   $214.7337   $214.73   $214.75   $214.70  
  Purchase #6 $66.95   13.626%   $76.0726   $76.07   $76.05   $76.10  
  Purchase #7 $108.90   4.744%   $114.0662   $114.07   $114.05   $114.10  
  7 purchase totals = $798.44       $875.9935   $875.99   $875.95   $876.00