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	$134.59	3.834%	$139.7502	$139.75	$139.75	$139.80
Purchase #2	$67.50	6.832%	$72.1116	$72.11	$72.10	$72.10
Purchase #3	$163.60	7.130%	$175.2647	$175.26	$175.25	$175.30
Purchase #4	$207.81	9.867%	$228.3146	$228.31	$228.30	$228.30
Purchase #5	$191.81	9.297%	$209.6426	$209.64	$209.65	$209.60
Purchase #6	$132.85	11.563%	$148.2114	$148.21	$148.20	$148.20
Purchase #7	$188.61	4.191%	$196.5146	$196.51	$196.50	$196.50
7 purchase totals =	$1,086.77		$1,169.8097	$1,169.79	$1,169.75	$1,169.80