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	$128.91	6.303%	$137.0352	$137.04	$137.05	$137.00
Purchase #2	$16.87	4.342%	$17.6025	$17.60	$17.60	$17.60
Purchase #3	$16.51	11.326%	$18.3799	$18.38	$18.40	$18.40
Purchase #4	$54.90	12.460%	$61.7405	$61.74	$61.75	$61.70
Purchase #5	$175.76	3.825%	$182.4828	$182.48	$182.50	$182.50
Purchase #6	$99.40	5.335%	$104.703	$104.70	$104.70	$104.70
Purchase #7	$34.72	7.705%	$37.3952	$37.40	$37.40	$37.40
7 purchase totals =	$527.07		$559.3391	$559.34	$559.40	$559.30