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	$173.73	9.651%	$190.4967	$190.50	$190.50	$190.50
Purchase #2	$157.53	6.279%	$167.4213	$167.42	$167.40	$167.40
Purchase #3	$58.51	4.326%	$61.0411	$61.04	$61.05	$61.00
Purchase #4	$227.52	3.305%	$235.0395	$235.04	$235.05	$235.00
Purchase #5	$85.92	3.668%	$89.0715	$89.07	$89.05	$89.10
Purchase #6	$53.91	3.471%	$55.7812	$55.78	$55.80	$55.80
Purchase #7	$171.49	11.376%	$190.9987	$191.00	$191.00	$191.00
7 purchase totals =	$928.61		$989.8500	$989.85	$989.85	$989.80