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	$234.94	6.184%	$249.4687	$249.47	$249.45	$249.50
Purchase #2	$162.42	6.686%	$173.2794	$173.28	$173.30	$173.30
Purchase #3	$156.78	10.474%	$173.2011	$173.20	$173.20	$173.20
Purchase #4	$195.50	7.373%	$209.9142	$209.91	$209.90	$209.90
Purchase #5	$162.60	8.564%	$176.5251	$176.53	$176.55	$176.50
Purchase #6	$92.60	8.859%	$100.8034	$100.80	$100.80	$100.80
Purchase #7	$244.43	4.545%	$255.5393	$255.54	$255.55	$255.50
7 purchase totals =	$1,249.27		$1,338.7312	$1,338.73	$1,338.75	$1,338.70