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	$31.47	5.103%	$33.0759	$33.08	$33.10	$33.10
Purchase #2	$31.82	9.814%	$34.9428	$34.94	$34.95	$34.90
Purchase #3	$116.59	9.182%	$127.2953	$127.30	$127.30	$127.30
Purchase #4	$91.72	5.659%	$96.9104	$96.91	$96.90	$96.90
Purchase #5	$159.44	12.799%	$179.8467	$179.85	$179.85	$179.80
Purchase #6	$21.83	3.756%	$22.6499	$22.65	$22.65	$22.60
Purchase #7	$206.31	9.109%	$225.1028	$225.10	$225.10	$225.10
7 purchase totals =	$659.18		$719.8238	$719.83	$719.85	$719.70