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	$78.49	5.333%	$82.6759	$82.68	$82.70	$82.70
Purchase #2	$167.26	13.355%	$189.5976	$189.60	$189.60	$189.60
Purchase #3	$20.44	8.413%	$22.1596	$22.16	$22.15	$22.20
Purchase #4	$85.30	11.806%	$95.3705	$95.37	$95.35	$95.40
Purchase #5	$143.45	4.834%	$150.3844	$150.38	$150.40	$150.40
Purchase #6	$63.46	13.574%	$72.0741	$72.07	$72.05	$72.10
Purchase #7	$243.87	12.329%	$273.9367	$273.94	$273.95	$273.90
7 purchase totals =	$802.27		$886.1988	$886.20	$886.20	$886.30