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	$59.87	7.859%	$64.5752	$64.58	$64.60	$64.60
Purchase #2	$184.83	4.440%	$193.0365	$193.04	$193.05	$193.00
Purchase #3	$198.87	11.820%	$222.3764	$222.38	$222.40	$222.40
Purchase #4	$11.28	6.717%	$12.0377	$12.04	$12.05	$12.00
Purchase #5	$173.69	3.185%	$179.222	$179.22	$179.20	$179.20
Purchase #6	$37.60	6.462%	$40.0297	$40.03	$40.05	$40.00
Purchase #7	$100.37	7.321%	$107.7181	$107.72	$107.70	$107.70
7 purchase totals =	$766.51		$818.9956	$819.01	$819.05	$818.90