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 $223.79   7.582%   $240.7578   $240.76   $240.75   $240.80  
  Purchase #2 $207.62   4.624%   $217.2203   $217.22   $217.20   $217.20  
  Purchase #3 $199.29   4.773%   $208.8021   $208.80   $208.80   $208.80  
  Purchase #4 $33.32   6.473%   $35.4768   $35.48   $35.50   $35.50  
  Purchase #5 $196.50   13.852%   $223.7192   $223.72   $223.70   $223.70  
  Purchase #6 $234.56   3.721%   $243.288   $243.29   $243.30   $243.30  
  Purchase #7 $236.41   4.284%   $246.5378   $246.54   $246.55   $246.50  
  7 purchase totals = $1,331.49       $1,415.8020   $1,415.81   $1,415.80   $1,415.80