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	$81.99	10.695%	$90.7588	$90.76	$90.75	$90.80
Purchase #2	$179.86	11.210%	$200.0223	$200.02	$200.00	$200.00
Purchase #3	$18.92	4.631%	$19.7962	$19.80	$19.80	$19.80
Purchase #4	$158.27	13.272%	$179.2756	$179.28	$179.30	$179.30
Purchase #5	$209.40	3.319%	$216.35	$216.35	$216.35	$216.40
Purchase #6	$223.95	10.325%	$247.0728	$247.07	$247.05	$247.10
Purchase #7	$167.79	13.319%	$190.138	$190.14	$190.15	$190.10
7 purchase totals =	$1,040.18		$1,143.4137	$1,143.42	$1,143.40	$1,143.50