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	$92.52	12.301%	$103.9009	$103.90	$103.90	$103.90
Purchase #2	$133.98	11.718%	$149.6798	$149.68	$149.70	$149.70
Purchase #3	$173.92	13.167%	$196.82	$196.82	$196.80	$196.80
Purchase #4	$246.56	3.681%	$255.6359	$255.64	$255.65	$255.60
Purchase #5	$128.56	5.774%	$135.9831	$135.98	$136.00	$136.00
Purchase #6	$70.88	7.789%	$76.4008	$76.40	$76.40	$76.40
Purchase #7	$243.51	4.475%	$254.4071	$254.41	$254.40	$254.40
7 purchase totals =	$1,089.93		$1,172.8276	$1,172.83	$1,172.85	$1,172.80