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	$143.52	8.556%	$155.7996	$155.80	$155.80	$155.80
Purchase #2	$82.59	8.753%	$89.8191	$89.82	$89.80	$89.80
Purchase #3	$89.75	7.834%	$96.781	$96.78	$96.80	$96.80
Purchase #4	$77.79	6.414%	$82.7795	$82.78	$82.80	$82.80
Purchase #5	$148.59	8.186%	$160.7536	$160.75	$160.75	$160.80
Purchase #6	$69.63	7.831%	$75.0827	$75.08	$75.10	$75.10
Purchase #7	$74.69	3.437%	$77.2571	$77.26	$77.25	$77.30
7 purchase totals =	$686.56		$738.2726	$738.27	$738.30	$738.40