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 $30.67   12.608%   $34.5369   $34.54   $34.55   $34.50  
  Purchase #2 $227.86   11.710%   $254.5424   $254.54   $254.55   $254.50  
  Purchase #3 $18.91   8.661%   $20.5478   $20.55   $20.55   $20.50  
  Purchase #4 $97.61   4.646%   $102.145   $102.15   $102.15   $102.10  
  Purchase #5 $46.42   5.725%   $49.0775   $49.08   $49.10   $49.10  
  Purchase #6 $66.81   4.407%   $69.7543   $69.75   $69.75   $69.80  
  Purchase #7 $205.78   13.451%   $233.4595   $233.46   $233.45   $233.50  
  7 purchase totals = $694.06       $764.0634   $764.07   $764.10   $764.00