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	$19.72	4.448%	$20.5971	$20.60	$20.60	$20.60
Purchase #2	$35.95	10.602%	$39.7614	$39.76	$39.75	$39.80
Purchase #3	$11.59	5.852%	$12.2682	$12.27	$12.25	$12.30
Purchase #4	$69.89	3.218%	$72.1391	$72.14	$72.15	$72.10
Purchase #5	$178.45	6.456%	$189.9707	$189.97	$189.95	$190.00
Purchase #6	$200.75	13.726%	$228.3049	$228.30	$228.30	$228.30
Purchase #7	$196.44	5.305%	$206.8611	$206.86	$206.85	$206.90
7 purchase totals =	$712.79		$769.9025	$769.90	$769.85	$770.00