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	$37.99	11.429%	$42.3319	$42.33	$42.35	$42.30
Purchase #2	$23.33	9.141%	$25.4626	$25.46	$25.45	$25.50
Purchase #3	$54.75	10.619%	$60.5639	$60.56	$60.55	$60.60
Purchase #4	$215.40	8.313%	$233.3062	$233.31	$233.30	$233.30
Purchase #5	$181.95	4.641%	$190.3943	$190.39	$190.40	$190.40
Purchase #6	$11.70	13.705%	$13.3035	$13.30	$13.30	$13.30
Purchase #7	$47.63	13.247%	$53.9395	$53.94	$53.95	$53.90
7 purchase totals =	$572.75		$619.3019	$619.29	$619.30	$619.30