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	$231.88	4.635%	$242.6276	$242.63	$242.65	$242.60
Purchase #2	$151.71	5.765%	$160.4561	$160.46	$160.45	$160.50
Purchase #3	$120.37	3.621%	$124.7286	$124.73	$124.75	$124.70
Purchase #4	$48.83	13.479%	$55.4118	$55.41	$55.40	$55.40
Purchase #5	$167.94	13.620%	$190.8134	$190.81	$190.80	$190.80
Purchase #6	$133.37	13.606%	$151.5163	$151.52	$151.50	$151.50
Purchase #7	$136.26	10.360%	$150.3765	$150.38	$150.40	$150.40
7 purchase totals =	$990.36		$1,075.9303	$1,075.94	$1,075.95	$1,075.90