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 $210.81   13.813%   $239.9292   $239.93   $239.95   $239.90  
  Purchase #2 $234.70   4.149%   $244.4377   $244.44   $244.45   $244.40  
  Purchase #3 $159.34   11.539%   $177.7262   $177.73   $177.75   $177.70  
  Purchase #4 $167.63   3.806%   $174.01   $174.01   $174.00   $174.00  
  Purchase #5 $147.48   6.167%   $156.5751   $156.58   $156.60   $156.60  
  Purchase #6 $69.25   5.340%   $72.948   $72.95   $72.95   $72.90  
  Purchase #7 $15.35   8.431%   $16.6442   $16.64   $16.65   $16.60  
  7 purchase totals = $1,004.56       $1,082.2704   $1,082.28   $1,082.35   $1,082.10