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 $114.64   8.240%   $124.0863   $124.09   $124.10   $124.10  
  Purchase #2 $171.46   8.387%   $185.8404   $185.84   $185.85   $185.80  
  Purchase #3 $48.81   4.409%   $50.962   $50.96   $50.95   $51.00  
  Purchase #4 $80.40   13.371%   $91.1503   $91.15   $91.15   $91.20  
  Purchase #5 $11.95   3.858%   $12.411   $12.41   $12.40   $12.40  
  Purchase #6 $225.66   4.716%   $236.3021   $236.30   $236.30   $236.30  
  Purchase #7 $91.81   9.197%   $100.2538   $100.25   $100.25   $100.30  
  7 purchase totals = $744.73       $801.0059   $801.00   $801.00   $801.10