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 $24.53   7.559%   $26.3842   $26.38   $26.40   $26.40  
  Purchase #2 $126.46   3.781%   $131.2415   $131.24   $131.25   $131.20  
  Purchase #3 $5.78   8.868%   $6.2926   $6.29   $6.30   $6.30  
  Purchase #4 $154.42   4.689%   $161.6608   $161.66   $161.65   $161.70  
  Purchase #5 $51.36   4.169%   $53.5012   $53.50   $53.50   $53.50  
  Purchase #6 $61.52   7.277%   $65.9968   $66.00   $66.00   $66.00  
  Purchase #7 $129.95   9.676%   $142.524   $142.52   $142.50   $142.50  
  7 purchase totals = $554.02       $587.6011   $587.59   $587.60   $587.60