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	$155.39	12.368%	$174.6086	$174.61	$174.60	$174.60
Purchase #2	$145.68	5.329%	$153.4433	$153.44	$153.45	$153.40
Purchase #3	$58.92	4.782%	$61.7376	$61.74	$61.75	$61.70
Purchase #4	$39.62	6.164%	$42.0622	$42.06	$42.05	$42.10
Purchase #5	$88.66	3.221%	$91.5157	$91.52	$91.50	$91.50
Purchase #6	$223.82	8.113%	$241.9785	$241.98	$242.00	$242.00
Purchase #7	$99.83	9.168%	$108.9824	$108.98	$109.00	$109.00
7 purchase totals =	$811.92		$874.3283	$874.33	$874.35	$874.30