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 $144.78   13.197%   $163.8866   $163.89   $163.90   $163.90  
  Purchase #2 $188.30   4.534%   $196.8375   $196.84   $196.85   $196.80  
  Purchase #3 $55.43   7.129%   $59.3816   $59.38   $59.40   $59.40  
  Purchase #4 $226.94   13.559%   $257.7108   $257.71   $257.70   $257.70  
  Purchase #5 $245.37   13.291%   $277.9821   $277.98   $278.00   $278.00  
  Purchase #6 $187.65   9.865%   $206.1617   $206.16   $206.15   $206.20  
  Purchase #7 $173.77   10.835%   $192.598   $192.60   $192.60   $192.60  
  7 purchase totals = $1,222.24       $1,354.5583   $1,354.56   $1,354.60   $1,354.60