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	$229.49	6.552%	$244.5262	$244.53	$244.55	$244.50
Purchase #2	$170.58	4.533%	$178.3124	$178.31	$178.30	$178.30
Purchase #3	$146.95	5.818%	$155.4996	$155.50	$155.50	$155.50
Purchase #4	$49.27	8.351%	$53.3845	$53.38	$53.40	$53.40
Purchase #5	$21.66	4.141%	$22.5569	$22.56	$22.55	$22.60
Purchase #6	$69.79	12.188%	$78.296	$78.30	$78.30	$78.30
Purchase #7	$75.62	13.524%	$85.8468	$85.85	$85.85	$85.80
7 purchase totals =	$763.36		$818.4224	$818.43	$818.45	$818.40