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	$234.44	3.617%	$242.9197	$242.92	$242.90	$242.90
Purchase #2	$22.33	13.769%	$25.4046	$25.40	$25.40	$25.40
Purchase #3	$170.69	6.754%	$182.2184	$182.22	$182.20	$182.20
Purchase #4	$139.79	13.420%	$158.5498	$158.55	$158.55	$158.50
Purchase #5	$87.27	3.310%	$90.1586	$90.16	$90.15	$90.20
Purchase #6	$166.44	10.729%	$184.2973	$184.30	$184.30	$184.30
Purchase #7	$158.85	8.357%	$172.1251	$172.13	$172.15	$172.10
7 purchase totals =	$979.81		$1,055.6735	$1,055.68	$1,055.65	$1,055.60