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	$25.64	11.596%	$28.6132	$28.61	$28.60	$28.60
Purchase #2	$196.31	6.529%	$209.1271	$209.13	$209.15	$209.10
Purchase #3	$32.51	3.347%	$33.5981	$33.60	$33.60	$33.60
Purchase #4	$30.96	12.466%	$34.8195	$34.82	$34.80	$34.80
Purchase #5	$242.93	13.320%	$275.2883	$275.29	$275.30	$275.30
Purchase #6	$197.69	11.717%	$220.8533	$220.85	$220.85	$220.90
Purchase #7	$41.58	5.415%	$43.8316	$43.83	$43.85	$43.80
7 purchase totals =	$767.62		$846.1311	$846.13	$846.15	$846.10