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	$30.30	6.442%	$32.2519	$32.25	$32.25	$32.30
Purchase #2	$18.75	5.540%	$19.7888	$19.79	$19.80	$19.80
Purchase #3	$50.42	13.808%	$57.382	$57.38	$57.40	$57.40
Purchase #4	$123.91	5.359%	$130.5503	$130.55	$130.55	$130.60
Purchase #5	$110.45	12.212%	$123.9382	$123.94	$123.95	$123.90
Purchase #6	$147.87	13.867%	$168.3751	$168.38	$168.40	$168.40
Purchase #7	$46.67	7.194%	$50.0274	$50.03	$50.05	$50.00
7 purchase totals =	$528.37		$582.3137	$582.32	$582.40	$582.40