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	$68.60	6.621%	$73.142	$73.14	$73.15	$73.10
Purchase #2	$97.32	4.623%	$101.8191	$101.82	$101.80	$101.80
Purchase #3	$99.61	8.524%	$108.1008	$108.10	$108.10	$108.10
Purchase #4	$17.92	6.637%	$19.1094	$19.11	$19.10	$19.10
Purchase #5	$43.85	3.338%	$45.3137	$45.31	$45.30	$45.30
Purchase #6	$29.79	13.727%	$33.8793	$33.88	$33.90	$33.90
Purchase #7	$179.77	10.510%	$198.6638	$198.66	$198.65	$198.70
7 purchase totals =	$536.86		$580.0281	$580.02	$580.00	$580.00