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	$79.77	13.211%	$90.3084	$90.31	$90.30	$90.30
Purchase #2	$54.75	12.520%	$61.6047	$61.60	$61.60	$61.60
Purchase #3	$201.46	9.286%	$220.1676	$220.17	$220.15	$220.20
Purchase #4	$179.70	5.716%	$189.9717	$189.97	$189.95	$190.00
Purchase #5	$6.77	8.449%	$7.342	$7.34	$7.35	$7.30
Purchase #6	$55.57	12.591%	$62.5668	$62.57	$62.55	$62.60
Purchase #7	$72.66	13.839%	$82.7154	$82.72	$82.70	$82.70
7 purchase totals =	$650.68		$714.6766	$714.68	$714.60	$714.70