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 $60.47   11.468%   $67.4047   $67.40   $67.40   $67.40  
  Purchase #2 $221.65   8.820%   $241.1995   $241.20   $241.20   $241.20  
  Purchase #3 $154.29   12.307%   $173.2785   $173.28   $173.30   $173.30  
  Purchase #4 $116.71   11.622%   $130.274   $130.27   $130.25   $130.30  
  Purchase #5 $31.84   6.685%   $33.9685   $33.97   $33.95   $34.00  
  Purchase #6 $24.47   9.723%   $26.8492   $26.85   $26.85   $26.80  
  Purchase #7 $216.32   11.156%   $240.4527   $240.45   $240.45   $240.50  
  7 purchase totals = $825.75       $913.4271   $913.42   $913.40   $913.50