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 $248.68   4.653%   $260.2511   $260.25   $260.25   $260.30  
  Purchase #2 $241.93   10.777%   $268.0028   $268.00   $268.00   $268.00  
  Purchase #3 $171.49   9.669%   $188.0714   $188.07   $188.05   $188.10  
  Purchase #4 $169.91   11.393%   $189.2678   $189.27   $189.25   $189.30  
  Purchase #5 $102.84   4.536%   $107.5048   $107.50   $107.50   $107.50  
  Purchase #6 $5.57   8.623%   $6.0503   $6.05   $6.05   $6.10  
  Purchase #7 $212.95   3.708%   $220.8462   $220.85   $220.85   $220.80  
  7 purchase totals = $1,153.37       $1,239.9944   $1,239.99   $1,239.95   $1,240.10