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	$105.62	8.726%	$114.8364	$114.84	$114.85	$114.80
Purchase #2	$37.54	13.328%	$42.5433	$42.54	$42.55	$42.50
Purchase #3	$52.71	12.717%	$59.4131	$59.41	$59.40	$59.40
Purchase #4	$32.94	13.786%	$37.4811	$37.48	$37.50	$37.50
Purchase #5	$56.99	11.210%	$63.3786	$63.38	$63.40	$63.40
Purchase #6	$106.78	10.657%	$118.1595	$118.16	$118.15	$118.20
Purchase #7	$150.92	6.202%	$160.2801	$160.28	$160.30	$160.30
7 purchase totals =	$543.50		$596.0921	$596.09	$596.15	$596.10