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	$71.80	11.513%	$80.0663	$80.07	$80.05	$80.10
Purchase #2	$46.92	8.233%	$50.7829	$50.78	$50.80	$50.80
Purchase #3	$104.49	13.433%	$118.5261	$118.53	$118.55	$118.50
Purchase #4	$184.78	5.263%	$194.505	$194.51	$194.50	$194.50
Purchase #5	$144.71	9.204%	$158.0291	$158.03	$158.05	$158.00
Purchase #6	$211.74	4.637%	$221.5584	$221.56	$221.55	$221.60
Purchase #7	$53.63	11.481%	$59.7873	$59.79	$59.80	$59.80
7 purchase totals =	$818.07		$883.2551	$883.27	$883.30	$883.30