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	$101.83	7.318%	$109.2819	$109.28	$109.30	$109.30
Purchase #2	$29.59	9.243%	$32.325	$32.33	$32.35	$32.30
Purchase #3	$166.87	3.703%	$173.0492	$173.05	$173.05	$173.00
Purchase #4	$144.30	3.417%	$149.2307	$149.23	$149.25	$149.20
Purchase #5	$114.89	4.464%	$120.0187	$120.02	$120.00	$120.00
Purchase #6	$38.55	6.696%	$41.1313	$41.13	$41.15	$41.10
Purchase #7	$134.92	12.162%	$151.329	$151.33	$151.35	$151.30
7 purchase totals =	$730.95		$776.3658	$776.37	$776.45	$776.20