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	$95.39	4.796%	$99.9649	$99.96	$99.95	$100.00
Purchase #2	$189.39	9.530%	$207.4389	$207.44	$207.45	$207.40
Purchase #3	$133.30	6.542%	$142.0205	$142.02	$142.00	$142.00
Purchase #4	$163.54	5.476%	$172.4955	$172.50	$172.50	$172.50
Purchase #5	$236.87	7.760%	$255.2511	$255.25	$255.25	$255.30
Purchase #6	$167.27	9.632%	$183.3814	$183.38	$183.40	$183.40
Purchase #7	$114.28	13.393%	$129.5855	$129.59	$129.60	$129.60
7 purchase totals =	$1,100.04		$1,190.1378	$1,190.14	$1,190.15	$1,190.20