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	$146.43	5.794%	$154.9142	$154.91	$154.90	$154.90
Purchase #2	$34.92	12.457%	$39.27	$39.27	$39.25	$39.30
Purchase #3	$19.63	7.213%	$21.0459	$21.05	$21.05	$21.00
Purchase #4	$195.90	4.620%	$204.9506	$204.95	$204.95	$205.00
Purchase #5	$75.81	5.479%	$79.9636	$79.96	$79.95	$80.00
Purchase #6	$93.50	13.195%	$105.8373	$105.84	$105.85	$105.80
Purchase #7	$82.59	8.514%	$89.6217	$89.62	$89.60	$89.60
7 purchase totals =	$648.78		$695.6033	$695.60	$695.55	$695.60