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	$68.46	12.319%	$76.8936	$76.89	$76.90	$76.90
Purchase #2	$129.70	12.467%	$145.8697	$145.87	$145.85	$145.90
Purchase #3	$201.45	6.522%	$214.5886	$214.59	$214.60	$214.60
Purchase #4	$50.56	11.415%	$56.3314	$56.33	$56.35	$56.30
Purchase #5	$56.95	4.269%	$59.3812	$59.38	$59.40	$59.40
Purchase #6	$151.40	13.150%	$171.3091	$171.31	$171.30	$171.30
Purchase #7	$144.32	10.707%	$159.7723	$159.77	$159.75	$159.80
7 purchase totals =	$802.84		$884.1459	$884.14	$884.15	$884.20