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	$180.30	12.370%	$202.6031	$202.60	$202.60	$202.60
Purchase #2	$189.46	3.709%	$196.4871	$196.49	$196.50	$196.50
Purchase #3	$48.42	13.241%	$54.8313	$54.83	$54.85	$54.80
Purchase #4	$70.72	6.256%	$75.1442	$75.14	$75.15	$75.10
Purchase #5	$152.40	12.288%	$171.1269	$171.13	$171.15	$171.10
Purchase #6	$109.52	6.805%	$116.9728	$116.97	$116.95	$117.00
Purchase #7	$145.40	10.404%	$160.5274	$160.53	$160.55	$160.50
7 purchase totals =	$896.22		$977.6928	$977.69	$977.75	$977.60