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 $44.79   9.624%   $49.1006   $49.10   $49.10   $49.10  
  Purchase #2 $119.80   3.465%   $123.9511   $123.95   $123.95   $124.00  
  Purchase #3 $50.43   11.517%   $56.238   $56.24   $56.25   $56.20  
  Purchase #4 $199.52   11.214%   $221.8942   $221.89   $221.90   $221.90  
  Purchase #5 $186.75   10.495%   $206.3494   $206.35   $206.35   $206.30  
  Purchase #6 $191.95   7.456%   $206.2618   $206.26   $206.25   $206.30  
  Purchase #7 $46.42   7.735%   $50.0106   $50.01   $50.00   $50.00  
  7 purchase totals = $839.66       $913.8057   $913.80   $913.80   $913.80