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 $41.69   6.649%   $44.462   $44.46   $44.45   $44.50  
  Purchase #2 $137.94   6.233%   $146.5378   $146.54   $146.55   $146.50  
  Purchase #3 $217.71   3.274%   $224.8378   $224.84   $224.85   $224.80  
  Purchase #4 $7.65   10.239%   $8.4333   $8.43   $8.45   $8.40  
  Purchase #5 $6.58   8.846%   $7.1621   $7.16   $7.15   $7.20  
  Purchase #6 $214.69   5.269%   $226.002   $226.00   $226.00   $226.00  
  Purchase #7 $99.57   9.361%   $108.8907   $108.89   $108.90   $108.90  
  7 purchase totals = $725.83       $766.3257   $766.32   $766.35   $766.30