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 $218.78   10.849%   $242.5154   $242.52   $242.50   $242.50  
  Purchase #2 $23.37   13.589%   $26.5457   $26.55   $26.55   $26.50  
  Purchase #3 $23.88   5.115%   $25.1015   $25.10   $25.10   $25.10  
  Purchase #4 $129.37   3.382%   $133.7453   $133.75   $133.75   $133.70  
  Purchase #5 $153.86   9.317%   $168.1951   $168.20   $168.20   $168.20  
  Purchase #6 $31.99   10.820%   $35.4513   $35.45   $35.45   $35.50  
  Purchase #7 $247.31   3.391%   $255.6963   $255.70   $255.70   $255.70  
  7 purchase totals = $828.56       $887.2506   $887.27   $887.25   $887.20