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	$109.47	7.600%	$117.7897	$117.79	$117.80	$117.80
Purchase #2	$158.27	13.277%	$179.2835	$179.28	$179.30	$179.30
Purchase #3	$167.99	10.157%	$185.0527	$185.05	$185.05	$185.10
Purchase #4	$63.54	6.794%	$67.8569	$67.86	$67.85	$67.90
Purchase #5	$153.43	7.422%	$164.8176	$164.82	$164.80	$164.80
Purchase #6	$38.84	10.235%	$42.8153	$42.82	$42.80	$42.80
Purchase #7	$109.54	10.653%	$121.2093	$121.21	$121.20	$121.20
7 purchase totals =	$801.08		$878.8250	$878.83	$878.80	$878.90