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	$204.38	12.620%	$230.1728	$230.17	$230.15	$230.20
Purchase #2	$234.39	4.350%	$244.586	$244.59	$244.60	$244.60
Purchase #3	$69.39	12.521%	$78.0783	$78.08	$78.10	$78.10
Purchase #4	$165.85	13.440%	$188.1402	$188.14	$188.15	$188.10
Purchase #5	$27.29	7.758%	$29.4072	$29.41	$29.40	$29.40
Purchase #6	$160.25	5.162%	$168.5221	$168.52	$168.50	$168.50
Purchase #7	$74.90	8.832%	$81.5152	$81.52	$81.50	$81.50
7 purchase totals =	$936.45		$1,020.4218	$1,020.43	$1,020.40	$1,020.40