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 $10.77   6.874%   $11.5103   $11.51   $11.50   $11.50  
  Purchase #2 $240.98   3.700%   $249.8963   $249.90   $249.90   $249.90  
  Purchase #3 $57.47   8.817%   $62.5371   $62.54   $62.55   $62.50  
  Purchase #4 $53.36   13.141%   $60.372   $60.37   $60.35   $60.40  
  Purchase #5 $85.59   6.553%   $91.1987   $91.20   $91.20   $91.20  
  Purchase #6 $185.63   12.331%   $208.52   $208.52   $208.50   $208.50  
  Purchase #7 $89.82   6.512%   $95.6691   $95.67   $95.65   $95.70  
  7 purchase totals = $723.62       $779.7035   $779.71   $779.65   $779.70