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	$249.48	11.454%	$278.0554	$278.06	$278.05	$278.10
Purchase #2	$25.51	6.663%	$27.2097	$27.21	$27.20	$27.20
Purchase #3	$78.50	13.399%	$89.0182	$89.02	$89.00	$89.00
Purchase #4	$217.38	9.863%	$238.8202	$238.82	$238.80	$238.80
Purchase #5	$19.42	4.670%	$20.3269	$20.33	$20.35	$20.30
Purchase #6	$114.90	4.325%	$119.8694	$119.87	$119.85	$119.90
Purchase #7	$68.54	8.580%	$74.4207	$74.42	$74.40	$74.40
7 purchase totals =	$773.73		$847.7205	$847.73	$847.65	$847.70