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	$123.31	7.232%	$132.2278	$132.23	$132.25	$132.20
Purchase #2	$202.51	6.620%	$215.9162	$215.92	$215.90	$215.90
Purchase #3	$7.85	3.822%	$8.15	$8.15	$8.15	$8.20
Purchase #4	$165.26	4.359%	$172.4637	$172.46	$172.45	$172.50
Purchase #5	$76.30	5.870%	$80.7788	$80.78	$80.80	$80.80
Purchase #6	$179.87	13.536%	$204.2172	$204.22	$204.20	$204.20
Purchase #7	$32.93	13.336%	$37.3215	$37.32	$37.30	$37.30
7 purchase totals =	$788.03		$851.0752	$851.08	$851.05	$851.10