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	$181.89	3.107%	$187.5413	$187.54	$187.55	$187.50
Purchase #2	$61.61	9.448%	$67.4309	$67.43	$67.45	$67.40
Purchase #3	$147.46	7.509%	$158.5328	$158.53	$158.55	$158.50
Purchase #4	$41.48	3.771%	$43.0442	$43.04	$43.05	$43.00
Purchase #5	$102.92	3.211%	$106.2248	$106.22	$106.20	$106.20
Purchase #6	$49.91	6.560%	$53.1841	$53.18	$53.20	$53.20
Purchase #7	$199.87	6.339%	$212.5398	$212.54	$212.55	$212.50
7 purchase totals =	$785.14		$828.4979	$828.48	$828.55	$828.30