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 $244.96   7.613%   $263.6088   $263.61   $263.60   $263.60  
  Purchase #2 $98.50   4.839%   $103.2664   $103.27   $103.25   $103.30  
  Purchase #3 $10.68   6.353%   $11.3585   $11.36   $11.35   $11.40  
  Purchase #4 $214.63   8.212%   $232.2554   $232.26   $232.25   $232.30  
  Purchase #5 $33.64   3.252%   $34.734   $34.73   $34.75   $34.70  
  Purchase #6 $172.88   7.585%   $185.9929   $185.99   $186.00   $186.00  
  Purchase #7 $173.65   7.253%   $186.2448   $186.24   $186.25   $186.20  
  7 purchase totals = $948.94       $1,017.4608   $1,017.46   $1,017.45   $1,017.50