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	$245.35	4.160%	$255.5566	$255.56	$255.55	$255.60
Purchase #2	$131.69	12.722%	$148.4436	$148.44	$148.45	$148.40
Purchase #3	$98.64	12.150%	$110.6248	$110.62	$110.60	$110.60
Purchase #4	$104.91	6.373%	$111.5959	$111.60	$111.60	$111.60
Purchase #5	$75.69	3.225%	$78.131	$78.13	$78.15	$78.10
Purchase #6	$157.59	8.234%	$170.566	$170.57	$170.55	$170.60
Purchase #7	$33.60	13.673%	$38.1941	$38.19	$38.20	$38.20
7 purchase totals =	$847.47		$913.1120	$913.11	$913.10	$913.10