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	$172.80	13.522%	$196.166	$196.17	$196.15	$196.20
Purchase #2	$158.44	6.110%	$168.1207	$168.12	$168.10	$168.10
Purchase #3	$40.70	3.280%	$42.035	$42.04	$42.05	$42.00
Purchase #4	$55.35	10.684%	$61.2636	$61.26	$61.25	$61.30
Purchase #5	$103.49	5.734%	$109.4241	$109.42	$109.40	$109.40
Purchase #6	$46.31	11.323%	$51.5537	$51.55	$51.55	$51.60
Purchase #7	$23.41	13.809%	$26.6427	$26.64	$26.65	$26.60
7 purchase totals =	$600.50		$655.2058	$655.20	$655.15	$655.20