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 $89.37   5.362%   $94.162   $94.16   $94.15   $94.20  
  Purchase #2 $13.49   12.203%   $15.1362   $15.14   $15.15   $15.10  
  Purchase #3 $26.27   4.516%   $27.4564   $27.46   $27.45   $27.50  
  Purchase #4 $42.95   5.379%   $45.2603   $45.26   $45.25   $45.30  
  Purchase #5 $99.42   8.675%   $108.0447   $108.04   $108.05   $108.00  
  Purchase #6 $11.39   7.113%   $12.2002   $12.20   $12.20   $12.20  
  Purchase #7 $221.43   4.191%   $230.7101   $230.71   $230.70   $230.70  
  7 purchase totals = $504.32       $532.9699   $532.97   $532.95   $533.00