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 $217.69   11.410%   $242.5284   $242.53   $242.55   $242.50  
  Purchase #2 $239.58   13.529%   $271.9928   $271.99   $272.00   $272.00  
  Purchase #3 $51.58   10.833%   $57.1677   $57.17   $57.15   $57.20  
  Purchase #4 $192.33   6.515%   $204.8603   $204.86   $204.85   $204.90  
  Purchase #5 $246.81   3.698%   $255.937   $255.94   $255.95   $255.90  
  Purchase #6 $130.79   12.625%   $147.3022   $147.30   $147.30   $147.30  
  Purchase #7 $168.42   10.299%   $185.7656   $185.77   $185.75   $185.80  
  7 purchase totals = $1,247.20       $1,365.5540   $1,365.56   $1,365.55   $1,365.60