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	$238.69	13.130%	$270.03	$270.03	$270.05	$270.00
Purchase #2	$188.59	4.690%	$197.4349	$197.43	$197.45	$197.40
Purchase #3	$162.80	6.546%	$173.4569	$173.46	$173.45	$173.50
Purchase #4	$25.52	7.462%	$27.4243	$27.42	$27.40	$27.40
Purchase #5	$99.90	5.772%	$105.6662	$105.67	$105.65	$105.70
Purchase #6	$171.32	10.869%	$189.9408	$189.94	$189.95	$189.90
Purchase #7	$147.79	3.321%	$152.6981	$152.70	$152.70	$152.70
7 purchase totals =	$1,034.61		$1,116.6512	$1,116.65	$1,116.65	$1,116.60