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	$61.62	6.860%	$65.8471	$65.85	$65.85	$65.80
Purchase #2	$113.52	6.497%	$120.8954	$120.90	$120.90	$120.90
Purchase #3	$114.39	11.511%	$127.5574	$127.56	$127.55	$127.60
Purchase #4	$142.38	9.452%	$155.8378	$155.84	$155.85	$155.80
Purchase #5	$28.69	4.634%	$30.0195	$30.02	$30.00	$30.00
Purchase #6	$14.35	9.845%	$15.7628	$15.76	$15.75	$15.80
Purchase #7	$55.98	11.859%	$62.6187	$62.62	$62.60	$62.60
7 purchase totals =	$530.93		$578.5387	$578.55	$578.50	$578.50