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 $22.57   8.572%   $24.5047   $24.50   $24.50   $24.50  
  Purchase #2 $34.98   7.347%   $37.55   $37.55   $37.55   $37.60  
  Purchase #3 $21.46   5.646%   $22.6716   $22.67   $22.65   $22.70  
  Purchase #4 $131.69   8.302%   $142.6229   $142.62   $142.60   $142.60  
  Purchase #5 $109.95   7.193%   $117.8587   $117.86   $117.85   $117.90  
  Purchase #6 $137.87   7.257%   $147.8752   $147.88   $147.90   $147.90  
  Purchase #7 $25.56   4.292%   $26.657   $26.66   $26.65   $26.70  
  7 purchase totals = $484.08       $519.7401   $519.74   $519.70   $519.90