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	$10.88	11.158%	$12.094	$12.09	$12.10	$12.10
Purchase #2	$238.96	10.268%	$263.4964	$263.50	$263.50	$263.50
Purchase #3	$100.36	4.845%	$105.2224	$105.22	$105.20	$105.20
Purchase #4	$18.62	3.269%	$19.2287	$19.23	$19.25	$19.20
Purchase #5	$211.45	3.852%	$219.5951	$219.60	$219.60	$219.60
Purchase #6	$245.48	11.612%	$273.9851	$273.99	$274.00	$274.00
Purchase #7	$76.82	10.786%	$85.1058	$85.11	$85.10	$85.10
7 purchase totals =	$902.57		$978.7275	$978.74	$978.75	$978.70