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	$59.64	6.491%	$63.5112	$63.51	$63.50	$63.50
Purchase #2	$185.30	13.401%	$210.1321	$210.13	$210.15	$210.10
Purchase #3	$85.63	5.828%	$90.6205	$90.62	$90.60	$90.60
Purchase #4	$118.43	9.515%	$129.6986	$129.70	$129.70	$129.70
Purchase #5	$245.54	10.581%	$271.5206	$271.52	$271.50	$271.50
Purchase #6	$38.59	5.729%	$40.8008	$40.80	$40.80	$40.80
Purchase #7	$57.95	13.531%	$65.7912	$65.79	$65.80	$65.80
7 purchase totals =	$791.08		$872.0750	$872.07	$872.05	$872.00