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	$115.86	10.665%	$128.2165	$128.22	$128.20	$128.20
Purchase #2	$173.30	6.370%	$184.3392	$184.34	$184.35	$184.30
Purchase #3	$10.85	4.585%	$11.3475	$11.35	$11.35	$11.30
Purchase #4	$174.71	8.715%	$189.936	$189.94	$189.95	$189.90
Purchase #5	$64.29	5.211%	$67.6402	$67.64	$67.65	$67.60
Purchase #6	$88.91	11.272%	$98.9319	$98.93	$98.95	$98.90
Purchase #7	$116.87	8.753%	$127.0996	$127.10	$127.10	$127.10
7 purchase totals =	$744.79		$807.5109	$807.52	$807.55	$807.30