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	$79.97	3.224%	$82.5482	$82.55	$82.55	$82.50
Purchase #2	$132.57	9.456%	$145.1058	$145.11	$145.10	$145.10
Purchase #3	$106.25	4.536%	$111.0695	$111.07	$111.05	$111.10
Purchase #4	$88.66	4.601%	$92.7392	$92.74	$92.75	$92.70
Purchase #5	$133.92	9.256%	$146.3156	$146.32	$146.30	$146.30
Purchase #6	$97.66	3.802%	$101.373	$101.37	$101.35	$101.40
Purchase #7	$151.32	13.706%	$172.0599	$172.06	$172.05	$172.10
7 purchase totals =	$790.35		$851.2112	$851.22	$851.15	$851.20