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	$50.55	12.548%	$56.893	$56.89	$56.90	$56.90
Purchase #2	$34.62	9.704%	$37.9795	$37.98	$38.00	$38.00
Purchase #3	$77.50	5.621%	$81.8563	$81.86	$81.85	$81.90
Purchase #4	$199.32	5.286%	$209.8561	$209.86	$209.85	$209.90
Purchase #5	$233.66	8.838%	$254.3109	$254.31	$254.30	$254.30
Purchase #6	$25.83	9.695%	$28.3342	$28.33	$28.35	$28.30
Purchase #7	$92.27	8.286%	$99.9155	$99.92	$99.90	$99.90
7 purchase totals =	$713.75		$769.1455	$769.15	$769.15	$769.20