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	$100.55	10.795%	$111.4044	$111.40	$111.40	$111.40
Purchase #2	$19.72	5.342%	$20.7734	$20.77	$20.75	$20.80
Purchase #3	$46.69	12.276%	$52.4217	$52.42	$52.40	$52.40
Purchase #4	$124.39	10.749%	$137.7607	$137.76	$137.75	$137.80
Purchase #5	$202.84	13.685%	$230.5987	$230.60	$230.60	$230.60
Purchase #6	$76.43	5.814%	$80.8736	$80.87	$80.85	$80.90
Purchase #7	$25.62	5.371%	$26.9961	$27.00	$27.00	$27.00
7 purchase totals =	$596.24		$660.8286	$660.82	$660.75	$660.90