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	$72.82	7.499%	$78.2808	$78.28	$78.30	$78.30
Purchase #2	$186.27	12.110%	$208.8273	$208.83	$208.85	$208.80
Purchase #3	$149.81	7.193%	$160.5858	$160.59	$160.60	$160.60
Purchase #4	$237.70	11.722%	$265.5632	$265.56	$265.55	$265.60
Purchase #5	$141.40	13.498%	$160.4862	$160.49	$160.50	$160.50
Purchase #6	$173.75	8.319%	$188.2043	$188.20	$188.20	$188.20
Purchase #7	$222.65	9.790%	$244.4474	$244.45	$244.45	$244.40
7 purchase totals =	$1,184.40		$1,306.3950	$1,306.40	$1,306.45	$1,306.40