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	$74.28	12.133%	$83.2924	$83.29	$83.30	$83.30
Purchase #2	$39.59	3.424%	$40.9456	$40.95	$40.95	$40.90
Purchase #3	$107.79	8.666%	$117.1311	$117.13	$117.15	$117.10
Purchase #4	$170.74	7.388%	$183.3543	$183.35	$183.35	$183.40
Purchase #5	$95.65	8.155%	$103.4503	$103.45	$103.45	$103.50
Purchase #6	$64.31	9.632%	$70.5043	$70.50	$70.50	$70.50
Purchase #7	$69.27	12.457%	$77.899	$77.90	$77.90	$77.90
7 purchase totals =	$621.63		$676.5770	$676.57	$676.60	$676.60