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	$46.80	13.256%	$53.0038	$53.00	$53.00	$53.00
Purchase #2	$139.91	11.183%	$155.5561	$155.56	$155.55	$155.60
Purchase #3	$127.96	13.648%	$145.424	$145.42	$145.40	$145.40
Purchase #4	$145.80	6.604%	$155.4286	$155.43	$155.45	$155.40
Purchase #5	$56.47	5.203%	$59.4081	$59.41	$59.40	$59.40
Purchase #6	$74.92	8.574%	$81.3436	$81.34	$81.35	$81.30
Purchase #7	$149.30	6.508%	$159.0164	$159.02	$159.00	$159.00
7 purchase totals =	$741.16		$809.1806	$809.18	$809.15	$809.10