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	$85.34	5.137%	$89.7239	$89.72	$89.70	$89.70
Purchase #2	$161.90	10.469%	$178.8493	$178.85	$178.85	$178.80
Purchase #3	$98.53	13.583%	$111.9133	$111.91	$111.90	$111.90
Purchase #4	$196.52	7.300%	$210.866	$210.87	$210.85	$210.90
Purchase #5	$121.84	3.716%	$126.3676	$126.37	$126.35	$126.40
Purchase #6	$246.84	13.194%	$279.4081	$279.41	$279.40	$279.40
Purchase #7	$94.89	13.589%	$107.7846	$107.78	$107.80	$107.80
7 purchase totals =	$1,005.86		$1,104.9128	$1,104.91	$1,104.85	$1,104.90