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	$19.27	10.442%	$21.2822	$21.28	$21.30	$21.30
Purchase #2	$163.46	9.348%	$178.7402	$178.74	$178.75	$178.70
Purchase #3	$119.98	6.471%	$127.7439	$127.74	$127.75	$127.70
Purchase #4	$174.41	12.644%	$196.4624	$196.46	$196.45	$196.50
Purchase #5	$113.36	12.324%	$127.3305	$127.33	$127.35	$127.30
Purchase #6	$70.55	11.870%	$78.9243	$78.92	$78.90	$78.90
Purchase #7	$106.43	6.390%	$113.2309	$113.23	$113.25	$113.20
7 purchase totals =	$767.46		$843.7144	$843.70	$843.75	$843.60