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	$166.86	4.181%	$173.8364	$173.84	$173.85	$173.80
Purchase #2	$27.96	8.669%	$30.3839	$30.38	$30.40	$30.40
Purchase #3	$80.60	10.836%	$89.3338	$89.33	$89.35	$89.30
Purchase #4	$116.35	12.142%	$130.4772	$130.48	$130.50	$130.50
Purchase #5	$6.72	13.815%	$7.6484	$7.65	$7.65	$7.60
Purchase #6	$178.62	11.539%	$199.231	$199.23	$199.25	$199.20
Purchase #7	$29.87	6.510%	$31.8145	$31.81	$31.80	$31.80
7 purchase totals =	$606.98		$662.7252	$662.72	$662.80	$662.60