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	$247.89	3.445%	$256.4298	$256.43	$256.45	$256.40
Purchase #2	$169.58	6.547%	$180.6824	$180.68	$180.70	$180.70
Purchase #3	$153.38	13.175%	$173.5878	$173.59	$173.60	$173.60
Purchase #4	$198.80	7.501%	$213.712	$213.71	$213.70	$213.70
Purchase #5	$40.56	11.147%	$45.0812	$45.08	$45.10	$45.10
Purchase #6	$205.39	11.853%	$229.7349	$229.73	$229.75	$229.70
Purchase #7	$84.85	6.409%	$90.288	$90.29	$90.30	$90.30
7 purchase totals =	$1,100.45		$1,189.5161	$1,189.51	$1,189.60	$1,189.50