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 $142.77   13.427%   $161.9397   $161.94   $161.95   $161.90  
  Purchase #2 $218.95   6.613%   $233.4292   $233.43   $233.45   $233.40  
  Purchase #3 $200.44   3.756%   $207.9685   $207.97   $207.95   $208.00  
  Purchase #4 $228.95   5.798%   $242.2245   $242.22   $242.20   $242.20  
  Purchase #5 $109.43   8.456%   $118.6834   $118.68   $118.70   $118.70  
  Purchase #6 $149.66   8.194%   $161.9231   $161.92   $161.90   $161.90  
  Purchase #7 $66.88   5.756%   $70.7296   $70.73   $70.75   $70.70  
  7 purchase totals = $1,117.08       $1,196.8980   $1,196.89   $1,196.90   $1,196.80