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	$135.41	3.111%	$139.6226	$139.62	$139.60	$139.60
Purchase #2	$124.49	12.259%	$139.7512	$139.75	$139.75	$139.80
Purchase #3	$58.92	9.139%	$64.3047	$64.30	$64.30	$64.30
Purchase #4	$103.27	8.149%	$111.6855	$111.69	$111.70	$111.70
Purchase #5	$236.50	10.404%	$261.1055	$261.11	$261.10	$261.10
Purchase #6	$142.56	13.276%	$161.4863	$161.49	$161.50	$161.50
Purchase #7	$134.94	13.865%	$153.6494	$153.65	$153.65	$153.60
7 purchase totals =	$936.09		$1,031.6052	$1,031.61	$1,031.60	$1,031.60