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	$134.81	11.662%	$150.5315	$150.53	$150.55	$150.50
Purchase #2	$178.33	9.797%	$195.801	$195.80	$195.80	$195.80
Purchase #3	$9.33	11.424%	$10.3959	$10.40	$10.40	$10.40
Purchase #4	$138.44	4.841%	$145.1419	$145.14	$145.15	$145.10
Purchase #5	$165.91	4.411%	$173.2283	$173.23	$173.25	$173.20
Purchase #6	$72.88	13.202%	$82.5016	$82.50	$82.50	$82.50
Purchase #7	$102.67	4.157%	$106.938	$106.94	$106.95	$106.90
7 purchase totals =	$802.37		$864.5382	$864.54	$864.60	$864.40