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	$77.60	4.289%	$80.9283	$80.93	$80.95	$80.90
Purchase #2	$93.32	12.851%	$105.3126	$105.31	$105.30	$105.30
Purchase #3	$80.58	13.461%	$91.4269	$91.43	$91.45	$91.40
Purchase #4	$172.74	8.294%	$187.0671	$187.07	$187.05	$187.10
Purchase #5	$184.46	6.154%	$195.8117	$195.81	$195.80	$195.80
Purchase #6	$65.37	9.535%	$71.603	$71.60	$71.60	$71.60
Purchase #7	$99.37	12.135%	$111.4285	$111.43	$111.45	$111.40
7 purchase totals =	$773.44		$843.5781	$843.58	$843.60	$843.50