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	$5.46	8.351%	$5.916	$5.92	$5.90	$5.90
Purchase #2	$152.87	12.729%	$172.3288	$172.33	$172.35	$172.30
Purchase #3	$148.34	8.386%	$160.7798	$160.78	$160.80	$160.80
Purchase #4	$59.42	12.262%	$66.7061	$66.71	$66.70	$66.70
Purchase #5	$151.87	13.674%	$172.6367	$172.64	$172.65	$172.60
Purchase #6	$9.27	12.595%	$10.4376	$10.44	$10.45	$10.40
Purchase #7	$53.72	4.372%	$56.0686	$56.07	$56.05	$56.10
7 purchase totals =	$580.95		$644.8736	$644.89	$644.90	$644.80