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 $212.61   13.306%   $240.8999   $240.90   $240.90   $240.90  
  Purchase #2 $163.88   11.240%   $182.3001   $182.30   $182.30   $182.30  
  Purchase #3 $247.49   9.614%   $271.2837   $271.28   $271.30   $271.30  
  Purchase #4 $207.60   3.782%   $215.4514   $215.45   $215.45   $215.50  
  Purchase #5 $137.89   6.697%   $147.1245   $147.12   $147.10   $147.10  
  Purchase #6 $171.97   6.548%   $183.2306   $183.23   $183.25   $183.20  
  Purchase #7 $220.36   3.767%   $228.661   $228.66   $228.65   $228.70  
  7 purchase totals = $1,361.80       $1,468.9512   $1,468.94   $1,468.95   $1,469.00