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	4.140%	$188.2643	$188.26	$188.25	$188.30
Purchase #2	$46.42	13.813%	$52.832	$52.83	$52.85	$52.80
Purchase #3	$222.86	9.720%	$244.522	$244.52	$244.50	$244.50
Purchase #4	$71.27	8.486%	$77.318	$77.32	$77.30	$77.30
Purchase #5	$38.74	5.423%	$40.8409	$40.84	$40.85	$40.80
Purchase #6	$221.32	10.744%	$245.0986	$245.10	$245.10	$245.10
Purchase #7	$214.89	8.696%	$233.5768	$233.58	$233.60	$233.60
7 purchase totals =	$996.28		$1,082.4526	$1,082.45	$1,082.45	$1,082.40