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	$10.25	11.754%	$11.4548	$11.45	$11.45	$11.50
Purchase #2	$101.84	9.213%	$111.2225	$111.22	$111.20	$111.20
Purchase #3	$103.72	7.519%	$111.5187	$111.52	$111.50	$111.50
Purchase #4	$70.33	12.414%	$79.0608	$79.06	$79.05	$79.10
Purchase #5	$88.78	8.297%	$96.1461	$96.15	$96.15	$96.10
Purchase #6	$125.82	8.620%	$136.6657	$136.67	$136.65	$136.70
Purchase #7	$159.84	4.337%	$166.7723	$166.77	$166.75	$166.80
7 purchase totals =	$660.58		$712.8409	$712.84	$712.75	$712.90