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	$155.95	6.311%	$165.792	$165.79	$165.80	$165.80
Purchase #2	$45.83	13.235%	$51.8956	$51.90	$51.90	$51.90
Purchase #3	$207.66	10.647%	$229.7696	$229.77	$229.75	$229.80
Purchase #4	$106.93	6.717%	$114.1125	$114.11	$114.10	$114.10
Purchase #5	$104.60	6.625%	$111.5298	$111.53	$111.55	$111.50
Purchase #6	$19.41	9.609%	$21.2751	$21.28	$21.30	$21.30
Purchase #7	$58.36	13.321%	$66.1341	$66.13	$66.15	$66.10
7 purchase totals =	$698.74		$760.5087	$760.51	$760.55	$760.50