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	$37.38	7.171%	$40.0605	$40.06	$40.05	$40.10
Purchase #2	$51.41	7.512%	$55.2719	$55.27	$55.25	$55.30
Purchase #3	$90.77	7.482%	$97.5614	$97.56	$97.55	$97.60
Purchase #4	$47.69	12.390%	$53.5988	$53.60	$53.60	$53.60
Purchase #5	$135.94	13.260%	$153.9656	$153.97	$153.95	$154.00
Purchase #6	$197.90	7.250%	$212.2478	$212.25	$212.25	$212.20
Purchase #7	$70.48	10.854%	$78.1299	$78.13	$78.15	$78.10
7 purchase totals =	$631.57		$690.8359	$690.84	$690.80	$690.90