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	$31.40	7.823%	$33.8564	$33.86	$33.85	$33.90
Purchase #2	$194.82	10.516%	$215.3073	$215.31	$215.30	$215.30
Purchase #3	$9.72	4.349%	$10.1427	$10.14	$10.15	$10.10
Purchase #4	$89.93	11.660%	$100.4158	$100.42	$100.40	$100.40
Purchase #5	$211.49	7.293%	$226.914	$226.91	$226.90	$226.90
Purchase #6	$180.42	4.335%	$188.2412	$188.24	$188.25	$188.20
Purchase #7	$17.27	11.274%	$19.217	$19.22	$19.20	$19.20
7 purchase totals =	$735.05		$794.0944	$794.10	$794.05	$794.00