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 $24.28   8.268%   $26.2875   $26.29   $26.30   $26.30  
  Purchase #2 $76.87   10.525%   $84.9606   $84.96   $84.95   $85.00  
  Purchase #3 $82.26   12.683%   $92.693   $92.69   $92.70   $92.70  
  Purchase #4 $96.81   10.861%   $107.3245   $107.32   $107.30   $107.30  
  Purchase #5 $169.30   9.239%   $184.9416   $184.94   $184.95   $184.90  
  Purchase #6 $8.78   11.172%   $9.7609   $9.76   $9.75   $9.80  
  Purchase #7 $88.64   3.732%   $91.948   $91.95   $91.95   $91.90  
  7 purchase totals = $546.94       $597.9161   $597.91   $597.90   $597.90