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 $250.98   7.356%   $269.4421   $269.44   $269.45   $269.40  
  Purchase #2 $146.97   13.631%   $167.0035   $167.00   $167.00   $167.00  
  Purchase #3 $123.69   3.147%   $127.5825   $127.58   $127.60   $127.60  
  Purchase #4 $8.25   8.368%   $8.9404   $8.94   $8.95   $8.90  
  Purchase #5 $124.53   11.807%   $139.2333   $139.23   $139.25   $139.20  
  Purchase #6 $213.36   4.583%   $223.1383   $223.14   $223.15   $223.10  
  Purchase #7 $140.69   12.491%   $158.2636   $158.26   $158.25   $158.30  
  7 purchase totals = $1,008.47       $1,093.6037   $1,093.59   $1,093.65   $1,093.50