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	$250.62	6.412%	$266.6898	$266.69	$266.70	$266.70
Purchase #2	$101.34	9.662%	$111.1315	$111.13	$111.15	$111.10
Purchase #3	$220.73	5.333%	$232.5015	$232.50	$232.50	$232.50
Purchase #4	$139.81	6.381%	$148.7313	$148.73	$148.75	$148.70
Purchase #5	$54.96	11.283%	$61.1611	$61.16	$61.15	$61.20
Purchase #6	$120.42	6.743%	$128.5399	$128.54	$128.55	$128.50
Purchase #7	$171.28	4.103%	$178.3076	$178.31	$178.30	$178.30
7 purchase totals =	$1,059.16		$1,127.0627	$1,127.06	$1,127.10	$1,127.00