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	$206.83	6.702%	$220.6917	$220.69	$220.70	$220.70
Purchase #2	$242.74	8.857%	$264.2395	$264.24	$264.25	$264.20
Purchase #3	$103.31	10.601%	$114.2619	$114.26	$114.25	$114.30
Purchase #4	$13.94	4.438%	$14.5587	$14.56	$14.55	$14.60
Purchase #5	$87.75	3.164%	$90.5264	$90.53	$90.55	$90.50
Purchase #6	$64.43	10.619%	$71.2718	$71.27	$71.25	$71.30
Purchase #7	$47.98	11.679%	$53.5836	$53.58	$53.60	$53.60
7 purchase totals =	$766.98		$829.1336	$829.13	$829.15	$829.20