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	$14.70	6.856%	$15.7078	$15.71	$15.70	$15.70
Purchase #2	$210.73	11.481%	$234.9239	$234.92	$234.90	$234.90
Purchase #3	$46.75	4.456%	$48.8332	$48.83	$48.85	$48.80
Purchase #4	$223.87	10.486%	$247.345	$247.35	$247.35	$247.30
Purchase #5	$85.37	5.421%	$89.9979	$90.00	$90.00	$90.00
Purchase #6	$249.93	9.448%	$273.5434	$273.54	$273.55	$273.50
Purchase #7	$167.57	13.420%	$190.0579	$190.06	$190.05	$190.10
7 purchase totals =	$998.92		$1,100.4091	$1,100.41	$1,100.40	$1,100.30