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	$190.93	5.192%	$200.8431	$200.84	$200.85	$200.80
Purchase #2	$139.91	13.267%	$158.4719	$158.47	$158.45	$158.50
Purchase #3	$211.79	13.693%	$240.7904	$240.79	$240.80	$240.80
Purchase #4	$83.34	10.741%	$92.2915	$92.29	$92.30	$92.30
Purchase #5	$243.64	9.244%	$266.1621	$266.16	$266.15	$266.20
Purchase #6	$249.77	9.565%	$273.6605	$273.66	$273.65	$273.70
Purchase #7	$74.34	4.395%	$77.6072	$77.61	$77.60	$77.60
7 purchase totals =	$1,193.72		$1,309.8267	$1,309.82	$1,309.80	$1,309.90