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	$6.58	11.453%	$7.3336	$7.33	$7.35	$7.30
Purchase #2	$82.30	11.610%	$91.855	$91.86	$91.85	$91.90
Purchase #3	$60.75	7.762%	$65.4654	$65.47	$65.45	$65.50
Purchase #4	$71.52	6.327%	$76.0451	$76.05	$76.05	$76.00
Purchase #5	$228.43	4.133%	$237.871	$237.87	$237.85	$237.90
Purchase #6	$111.49	13.538%	$126.5835	$126.58	$126.60	$126.60
Purchase #7	$31.71	5.310%	$33.3938	$33.39	$33.40	$33.40
7 purchase totals =	$592.78		$638.5474	$638.55	$638.55	$638.60