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	$32.87	5.296%	$34.6108	$34.61	$34.60	$34.60
Purchase #2	$191.99	10.353%	$211.8667	$211.87	$211.85	$211.90
Purchase #3	$96.56	9.509%	$105.7419	$105.74	$105.75	$105.70
Purchase #4	$89.39	4.588%	$93.4912	$93.49	$93.50	$93.50
Purchase #5	$189.38	3.483%	$195.9761	$195.98	$196.00	$196.00
Purchase #6	$17.69	3.509%	$18.3107	$18.31	$18.30	$18.30
Purchase #7	$112.78	4.280%	$117.607	$117.61	$117.60	$117.60
7 purchase totals =	$730.66		$777.6044	$777.61	$777.60	$777.60