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 $213.28   12.458%   $239.8504   $239.85   $239.85   $239.90  
  Purchase #2 $211.29   11.339%   $235.2482   $235.25   $235.25   $235.20  
  Purchase #3 $248.43   13.482%   $281.9233   $281.92   $281.90   $281.90  
  Purchase #4 $45.50   10.132%   $50.1101   $50.11   $50.10   $50.10  
  Purchase #5 $150.65   8.180%   $162.9732   $162.97   $162.95   $163.00  
  Purchase #6 $127.31   6.730%   $135.878   $135.88   $135.90   $135.90  
  Purchase #7 $134.45   9.522%   $147.2523   $147.25   $147.25   $147.30  
  7 purchase totals = $1,130.91       $1,253.2355   $1,253.23   $1,253.20   $1,253.30