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	$139.52	8.499%	$151.3778	$151.38	$151.40	$151.40
Purchase #2	$46.77	7.607%	$50.3278	$50.33	$50.35	$50.30
Purchase #3	$186.73	13.729%	$212.3662	$212.37	$212.35	$212.40
Purchase #4	$101.90	9.195%	$111.2697	$111.27	$111.25	$111.30
Purchase #5	$200.99	11.770%	$224.6465	$224.65	$224.65	$224.60
Purchase #6	$70.80	12.414%	$79.5891	$79.59	$79.60	$79.60
Purchase #7	$5.54	4.376%	$5.7824	$5.78	$5.80	$5.80
7 purchase totals =	$752.25		$835.3595	$835.37	$835.40	$835.40