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 $37.40   11.434%   $41.6763   $41.68   $41.70   $41.70  
  Purchase #2 $198.57   8.732%   $215.9091   $215.91   $215.90   $215.90  
  Purchase #3 $109.99   4.127%   $114.5293   $114.53   $114.55   $114.50  
  Purchase #4 $175.36   4.156%   $182.648   $182.65   $182.65   $182.60  
  Purchase #5 $204.74   12.465%   $230.2608   $230.26   $230.25   $230.30  
  Purchase #6 $32.58   12.671%   $36.7082   $36.71   $36.70   $36.70  
  Purchase #7 $175.40   13.809%   $199.621   $199.62   $199.60   $199.60  
  7 purchase totals = $934.04       $1,021.3527   $1,021.36   $1,021.35   $1,021.30