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	$96.54	4.348%	$100.7376	$100.74	$100.75	$100.70
Purchase #2	$115.89	12.521%	$130.4006	$130.40	$130.40	$130.40
Purchase #3	$174.77	9.601%	$191.5497	$191.55	$191.55	$191.50
Purchase #4	$127.92	9.312%	$139.8319	$139.83	$139.85	$139.80
Purchase #5	$215.56	6.697%	$229.9961	$230.00	$230.00	$230.00
Purchase #6	$159.76	5.865%	$169.1299	$169.13	$169.15	$169.10
Purchase #7	$248.32	12.144%	$278.476	$278.48	$278.50	$278.50
7 purchase totals =	$1,138.76		$1,240.1218	$1,240.13	$1,240.20	$1,240.00