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	$73.98	11.167%	$82.2413	$82.24	$82.25	$82.20
Purchase #2	$144.92	9.459%	$158.628	$158.63	$158.65	$158.60
Purchase #3	$96.55	12.716%	$108.8273	$108.83	$108.85	$108.80
Purchase #4	$11.85	13.762%	$13.4808	$13.48	$13.50	$13.50
Purchase #5	$62.50	13.800%	$71.125	$71.13	$71.15	$71.10
Purchase #6	$159.88	7.690%	$172.1748	$172.17	$172.15	$172.20
Purchase #7	$6.25	3.624%	$6.4765	$6.48	$6.50	$6.50
7 purchase totals =	$555.93		$612.9537	$612.96	$613.05	$612.90