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	$128.81	4.507%	$134.6155	$134.62	$134.60	$134.60
Purchase #2	$80.57	11.257%	$89.6398	$89.64	$89.65	$89.60
Purchase #3	$223.39	4.447%	$233.3242	$233.32	$233.30	$233.30
Purchase #4	$33.87	4.649%	$35.4446	$35.44	$35.45	$35.40
Purchase #5	$46.25	10.604%	$51.1544	$51.15	$51.15	$51.20
Purchase #6	$42.31	13.202%	$47.8958	$47.90	$47.90	$47.90
Purchase #7	$137.63	12.692%	$155.098	$155.10	$155.10	$155.10
7 purchase totals =	$692.83		$747.1723	$747.17	$747.15	$747.10