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	$40.92	3.448%	$42.3309	$42.33	$42.35	$42.30
Purchase #2	$128.80	12.142%	$144.4389	$144.44	$144.45	$144.40
Purchase #3	$89.62	10.503%	$99.0328	$99.03	$99.05	$99.00
Purchase #4	$101.42	11.758%	$113.345	$113.35	$113.35	$113.30
Purchase #5	$166.59	5.492%	$175.7391	$175.74	$175.75	$175.70
Purchase #6	$187.78	8.809%	$204.3215	$204.32	$204.30	$204.30
Purchase #7	$121.49	7.468%	$130.5629	$130.56	$130.55	$130.60
7 purchase totals =	$836.62		$909.7711	$909.77	$909.80	$909.60