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	$35.58	6.169%	$37.7749	$37.77	$37.75	$37.80
Purchase #2	$59.76	10.139%	$65.8191	$65.82	$65.80	$65.80
Purchase #3	$190.56	11.173%	$211.8513	$211.85	$211.85	$211.90
Purchase #4	$161.45	7.726%	$173.9236	$173.92	$173.90	$173.90
Purchase #5	$200.84	3.778%	$208.4277	$208.43	$208.45	$208.40
Purchase #6	$118.44	7.576%	$127.413	$127.41	$127.40	$127.40
Purchase #7	$202.44	13.402%	$229.571	$229.57	$229.55	$229.60
7 purchase totals =	$969.07		$1,054.7806	$1,054.77	$1,054.70	$1,054.80