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	$180.86	3.666%	$187.4903	$187.49	$187.50	$187.50
Purchase #2	$140.67	5.513%	$148.4251	$148.43	$148.45	$148.40
Purchase #3	$74.57	7.411%	$80.0964	$80.10	$80.10	$80.10
Purchase #4	$209.62	7.483%	$225.3059	$225.31	$225.30	$225.30
Purchase #5	$56.52	6.647%	$60.2769	$60.28	$60.30	$60.30
Purchase #6	$92.42	8.348%	$100.1352	$100.14	$100.15	$100.10
Purchase #7	$52.42	13.739%	$59.622	$59.62	$59.60	$59.60
7 purchase totals =	$807.08		$861.3518	$861.37	$861.40	$861.30