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 $244.56   11.137%   $271.7966   $271.80   $271.80   $271.80  
  Purchase #2 $149.96   4.115%   $156.1309   $156.13   $156.15   $156.10  
  Purchase #3 $112.41   6.516%   $119.7346   $119.73   $119.75   $119.70  
  Purchase #4 $87.93   12.235%   $98.6882   $98.69   $98.70   $98.70  
  Purchase #5 $200.99   6.361%   $213.775   $213.78   $213.80   $213.80  
  Purchase #6 $248.89   9.522%   $272.5893   $272.59   $272.60   $272.60  
  Purchase #7 $212.77   7.806%   $229.3788   $229.38   $229.40   $229.40  
  7 purchase totals = $1,257.51       $1,362.0934   $1,362.10   $1,362.20   $1,362.10