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	$180.78	5.357%	$190.4644	$190.46	$190.45	$190.50
Purchase #2	$41.77	8.398%	$45.2778	$45.28	$45.30	$45.30
Purchase #3	$33.49	9.621%	$36.7121	$36.71	$36.70	$36.70
Purchase #4	$123.29	4.471%	$128.8023	$128.80	$128.80	$128.80
Purchase #5	$68.51	12.627%	$77.1608	$77.16	$77.15	$77.20
Purchase #6	$107.82	12.517%	$121.3158	$121.32	$121.30	$121.30
Purchase #7	$131.84	7.542%	$141.7834	$141.78	$141.80	$141.80
7 purchase totals =	$687.50		$741.5166	$741.51	$741.50	$741.60