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 $60.63   4.730%   $63.4978   $63.50   $63.50   $63.50  
  Purchase #2 $168.68   4.542%   $176.3414   $176.34   $176.35   $176.30  
  Purchase #3 $141.89   3.531%   $146.9001   $146.90   $146.90   $146.90  
  Purchase #4 $147.42   11.788%   $164.7979   $164.80   $164.80   $164.80  
  Purchase #5 $218.49   13.765%   $248.5651   $248.57   $248.55   $248.60  
  Purchase #6 $209.46   8.383%   $227.019   $227.02   $227.00   $227.00  
  Purchase #7 $211.77   4.421%   $221.1324   $221.13   $221.15   $221.10  
  7 purchase totals = $1,158.34       $1,248.2537   $1,248.26   $1,248.25   $1,248.20