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 $34.41   5.483%   $36.2967   $36.30   $36.30   $36.30  
  Purchase #2 $185.60   7.342%   $199.2268   $199.23   $199.25   $199.20  
  Purchase #3 $181.99   10.150%   $200.462   $200.46   $200.45   $200.50  
  Purchase #4 $237.26   10.644%   $262.514   $262.51   $262.50   $262.50  
  Purchase #5 $82.42   10.448%   $91.0312   $91.03   $91.05   $91.00  
  Purchase #6 $150.46   3.723%   $156.0616   $156.06   $156.05   $156.10  
  Purchase #7 $15.82   3.265%   $16.3365   $16.34   $16.35   $16.30  
  7 purchase totals = $887.96       $961.9288   $961.93   $961.95   $961.90