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	$101.86	7.437%	$109.4353	$109.44	$109.45	$109.40
Purchase #2	$120.29	7.173%	$128.9184	$128.92	$128.90	$128.90
Purchase #3	$61.28	7.423%	$65.8288	$65.83	$65.85	$65.80
Purchase #4	$139.45	3.675%	$144.5748	$144.57	$144.55	$144.60
Purchase #5	$240.35	5.824%	$254.348	$254.35	$254.35	$254.30
Purchase #6	$70.33	10.359%	$77.6155	$77.62	$77.60	$77.60
Purchase #7	$79.47	12.482%	$89.3894	$89.39	$89.40	$89.40
7 purchase totals =	$813.03		$870.1102	$870.12	$870.10	$870.00