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	$29.62	7.692%	$31.8984	$31.90	$31.90	$31.90
Purchase #2	$64.52	6.650%	$68.8106	$68.81	$68.80	$68.80
Purchase #3	$112.53	13.377%	$127.5831	$127.58	$127.60	$127.60
Purchase #4	$46.96	13.301%	$53.2061	$53.21	$53.20	$53.20
Purchase #5	$214.31	8.166%	$231.8106	$231.81	$231.80	$231.80
Purchase #6	$141.88	11.576%	$158.304	$158.30	$158.30	$158.30
Purchase #7	$29.78	13.341%	$33.7529	$33.75	$33.75	$33.80
7 purchase totals =	$639.60		$705.3657	$705.36	$705.35	$705.40