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	$101.61	9.417%	$111.1786	$111.18	$111.20	$111.20
Purchase #2	$130.63	11.243%	$145.3167	$145.32	$145.30	$145.30
Purchase #3	$165.51	10.369%	$182.6717	$182.67	$182.65	$182.70
Purchase #4	$194.61	11.714%	$217.4066	$217.41	$217.40	$217.40
Purchase #5	$38.53	5.795%	$40.7628	$40.76	$40.75	$40.80
Purchase #6	$57.66	12.496%	$64.8652	$64.87	$64.85	$64.90
Purchase #7	$77.89	4.132%	$81.1084	$81.11	$81.10	$81.10
7 purchase totals =	$766.44		$843.3100	$843.32	$843.25	$843.40