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	$220.59	13.479%	$250.3233	$250.32	$250.30	$250.30
Purchase #2	$246.34	10.542%	$272.3092	$272.31	$272.30	$272.30
Purchase #3	$5.52	6.408%	$5.8737	$5.87	$5.85	$5.90
Purchase #4	$53.69	4.727%	$56.2279	$56.23	$56.25	$56.20
Purchase #5	$180.64	10.265%	$199.1827	$199.18	$199.20	$199.20
Purchase #6	$234.58	3.137%	$241.9388	$241.94	$241.95	$241.90
Purchase #7	$70.37	6.194%	$74.7287	$74.73	$74.75	$74.70
7 purchase totals =	$1,011.73		$1,100.5843	$1,100.58	$1,100.60	$1,100.50