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	$149.72	11.300%	$166.6384	$166.64	$166.65	$166.60
Purchase #2	$141.80	8.733%	$154.1834	$154.18	$154.20	$154.20
Purchase #3	$244.42	12.597%	$275.2096	$275.21	$275.20	$275.20
Purchase #4	$36.41	4.575%	$38.0758	$38.08	$38.10	$38.10
Purchase #5	$113.33	12.163%	$127.1143	$127.11	$127.10	$127.10
Purchase #6	$38.81	6.296%	$41.2535	$41.25	$41.25	$41.30
Purchase #7	$104.82	7.250%	$112.4195	$112.42	$112.40	$112.40
7 purchase totals =	$829.31		$914.8945	$914.89	$914.90	$914.90