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	$58.64	11.567%	$65.4229	$65.42	$65.40	$65.40
Purchase #2	$199.92	11.613%	$223.1367	$223.14	$223.15	$223.10
Purchase #3	$37.72	11.847%	$42.1887	$42.19	$42.20	$42.20
Purchase #4	$91.57	8.232%	$99.108	$99.11	$99.10	$99.10
Purchase #5	$50.46	7.521%	$54.2551	$54.26	$54.25	$54.30
Purchase #6	$218.60	10.482%	$241.5137	$241.51	$241.50	$241.50
Purchase #7	$110.45	7.150%	$118.3472	$118.35	$118.35	$118.30
7 purchase totals =	$767.36		$843.9723	$843.98	$843.95	$843.90