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 $248.73   13.616%   $282.5971   $282.60   $282.60   $282.60  
  Purchase #2 $185.53   6.139%   $196.9197   $196.92   $196.90   $196.90  
  Purchase #3 $145.25   6.277%   $154.3673   $154.37   $154.35   $154.40  
  Purchase #4 $247.60   9.502%   $271.127   $271.13   $271.15   $271.10  
  Purchase #5 $116.54   8.769%   $126.7594   $126.76   $126.75   $126.80  
  Purchase #6 $150.47   12.604%   $169.4352   $169.44   $169.45   $169.40  
  Purchase #7 $76.27   9.856%   $83.7872   $83.79   $83.80   $83.80  
  7 purchase totals = $1,170.39       $1,284.9929   $1,285.01   $1,285.00   $1,285.00