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	$132.83	13.615%	$150.9148	$150.91	$150.90	$150.90
Purchase #2	$88.62	11.349%	$98.6775	$98.68	$98.70	$98.70
Purchase #3	$126.43	4.815%	$132.5176	$132.52	$132.50	$132.50
Purchase #4	$11.95	4.114%	$12.4416	$12.44	$12.45	$12.40
Purchase #5	$143.84	10.754%	$159.3086	$159.31	$159.30	$159.30
Purchase #6	$238.56	6.687%	$254.5125	$254.51	$254.50	$254.50
Purchase #7	$89.53	12.498%	$100.7195	$100.72	$100.70	$100.70
7 purchase totals =	$831.76		$909.0921	$909.09	$909.05	$909.00