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	$52.53	13.242%	$59.486	$59.49	$59.50	$59.50
Purchase #2	$194.91	6.126%	$206.8502	$206.85	$206.85	$206.90
Purchase #3	$44.97	9.566%	$49.2718	$49.27	$49.25	$49.30
Purchase #4	$16.27	12.762%	$18.3464	$18.35	$18.35	$18.30
Purchase #5	$12.42	7.262%	$13.3219	$13.32	$13.30	$13.30
Purchase #6	$97.62	12.538%	$109.8596	$109.86	$109.85	$109.90
Purchase #7	$62.26	11.623%	$69.4965	$69.50	$69.50	$69.50
7 purchase totals =	$480.98		$526.6324	$526.64	$526.60	$526.70