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	$19.41	3.633%	$20.1152	$20.12	$20.10	$20.10
Purchase #2	$53.80	4.439%	$56.1882	$56.19	$56.20	$56.20
Purchase #3	$138.91	6.722%	$148.2475	$148.25	$148.25	$148.20
Purchase #4	$106.86	10.684%	$118.2769	$118.28	$118.30	$118.30
Purchase #5	$183.75	8.377%	$199.1427	$199.14	$199.15	$199.10
Purchase #6	$83.59	8.418%	$90.6266	$90.63	$90.65	$90.60
Purchase #7	$118.28	6.578%	$126.0605	$126.06	$126.05	$126.10
7 purchase totals =	$704.60		$758.6576	$758.67	$758.70	$758.60