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	$173.64	3.232%	$179.252	$179.25	$179.25	$179.30
Purchase #2	$204.78	7.664%	$220.4743	$220.47	$220.45	$220.50
Purchase #3	$134.37	10.777%	$148.8511	$148.85	$148.85	$148.90
Purchase #4	$193.60	11.441%	$215.7498	$215.75	$215.75	$215.70
Purchase #5	$81.30	12.685%	$91.6129	$91.61	$91.60	$91.60
Purchase #6	$59.89	8.411%	$64.9273	$64.93	$64.95	$64.90
Purchase #7	$95.66	4.569%	$100.0307	$100.03	$100.05	$100.00
7 purchase totals =	$943.24		$1,020.8981	$1,020.89	$1,020.90	$1,020.90