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	$171.60	8.145%	$185.5768	$185.58	$185.60	$185.60
Purchase #2	$93.41	7.191%	$100.1271	$100.13	$100.15	$100.10
Purchase #3	$215.77	6.645%	$230.1079	$230.11	$230.10	$230.10
Purchase #4	$123.57	6.372%	$131.4439	$131.44	$131.45	$131.40
Purchase #5	$102.67	13.258%	$116.282	$116.28	$116.30	$116.30
Purchase #6	$154.88	7.552%	$166.5765	$166.58	$166.60	$166.60
Purchase #7	$154.44	3.393%	$159.6801	$159.68	$159.70	$159.70
7 purchase totals =	$1,016.34		$1,089.7943	$1,089.80	$1,089.90	$1,089.80