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	$47.69	9.695%	$52.3135	$52.31	$52.30	$52.30
Purchase #2	$84.76	3.712%	$87.9063	$87.91	$87.90	$87.90
Purchase #3	$248.55	3.309%	$256.7745	$256.77	$256.75	$256.80
Purchase #4	$146.73	6.485%	$156.2454	$156.25	$156.25	$156.20
Purchase #5	$166.95	11.172%	$185.6017	$185.60	$185.60	$185.60
Purchase #6	$250.45	11.257%	$278.6432	$278.64	$278.65	$278.60
Purchase #7	$48.87	13.550%	$55.4919	$55.49	$55.50	$55.50
7 purchase totals =	$994.00		$1,072.9765	$1,072.97	$1,072.95	$1,072.90