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	$99.74	6.363%	$106.0865	$106.09	$106.10	$106.10
Purchase #2	$45.37	7.753%	$48.8875	$48.89	$48.90	$48.90
Purchase #3	$99.62	12.171%	$111.7448	$111.74	$111.75	$111.70
Purchase #4	$78.30	7.259%	$83.9838	$83.98	$84.00	$84.00
Purchase #5	$79.67	13.157%	$90.1522	$90.15	$90.15	$90.20
Purchase #6	$171.66	4.153%	$178.789	$178.79	$178.80	$178.80
Purchase #7	$55.35	10.761%	$61.3062	$61.31	$61.30	$61.30
7 purchase totals =	$629.71		$680.9500	$680.95	$681.00	$681.00