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 $244.26   10.554%   $270.0392   $270.04   $270.05   $270.00  
  Purchase #2 $196.27   7.310%   $210.6173   $210.62   $210.60   $210.60  
  Purchase #3 $240.64   9.268%   $262.9425   $262.94   $262.95   $262.90  
  Purchase #4 $247.46   4.606%   $258.858   $258.86   $258.85   $258.90  
  Purchase #5 $194.47   9.865%   $213.6545   $213.65   $213.65   $213.70  
  Purchase #6 $223.71   13.777%   $254.5305   $254.53   $254.55   $254.50  
  Purchase #7 $150.91   7.299%   $161.9249   $161.92   $161.90   $161.90  
  7 purchase totals = $1,497.72       $1,632.5669   $1,632.56   $1,632.55   $1,632.50