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	$31.27	9.429%	$34.2184	$34.22	$34.20	$34.20
Purchase #2	$244.65	12.642%	$275.5787	$275.58	$275.60	$275.60
Purchase #3	$78.58	4.828%	$82.3738	$82.37	$82.35	$82.40
Purchase #4	$136.63	3.520%	$141.4394	$141.44	$141.45	$141.40
Purchase #5	$101.80	10.307%	$112.2925	$112.29	$112.30	$112.30
Purchase #6	$243.28	12.461%	$273.5951	$273.60	$273.60	$273.60
Purchase #7	$183.28	5.199%	$192.8087	$192.81	$192.80	$192.80
7 purchase totals =	$1,019.49		$1,112.3066	$1,112.31	$1,112.30	$1,112.30