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 $248.80   10.157%   $274.0706   $274.07   $274.05   $274.10  
  Purchase #2 $69.80   6.297%   $74.1953   $74.20   $74.20   $74.20  
  Purchase #3 $241.73   10.763%   $267.7474   $267.75   $267.75   $267.70  
  Purchase #4 $112.69   3.666%   $116.8212   $116.82   $116.80   $116.80  
  Purchase #5 $159.55   8.657%   $173.3622   $173.36   $173.35   $173.40  
  Purchase #6 $202.50   9.530%   $221.7983   $221.80   $221.80   $221.80  
  Purchase #7 $123.98   7.661%   $133.4781   $133.48   $133.50   $133.50  
  7 purchase totals = $1,159.05       $1,261.4731   $1,261.48   $1,261.45   $1,261.50