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 $23.40   12.296%   $26.2773   $26.28   $26.30   $26.30  
  Purchase #2 $135.79   5.279%   $142.9584   $142.96   $142.95   $143.00  
  Purchase #3 $59.66   10.135%   $65.7065   $65.71   $65.70   $65.70  
  Purchase #4 $26.37   4.665%   $27.6002   $27.60   $27.60   $27.60  
  Purchase #5 $155.59   8.177%   $168.3126   $168.31   $168.30   $168.30  
  Purchase #6 $80.79   7.451%   $86.8097   $86.81   $86.80   $86.80  
  Purchase #7 $215.60   12.639%   $242.8497   $242.85   $242.85   $242.80  
  7 purchase totals = $697.20       $760.5144   $760.52   $760.50   $760.50