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	$29.74	5.649%	$31.42	$31.42	$31.40	$31.40
Purchase #2	$205.34	6.213%	$218.0978	$218.10	$218.10	$218.10
Purchase #3	$42.39	7.806%	$45.699	$45.70	$45.70	$45.70
Purchase #4	$155.77	12.544%	$175.3098	$175.31	$175.30	$175.30
Purchase #5	$128.50	12.107%	$144.0575	$144.06	$144.05	$144.10
Purchase #6	$20.35	11.231%	$22.6355	$22.64	$22.65	$22.60
Purchase #7	$162.40	6.146%	$172.3811	$172.38	$172.40	$172.40
7 purchase totals =	$744.49		$809.6007	$809.61	$809.60	$809.60