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	$165.32	11.422%	$184.2029	$184.20	$184.20	$184.20
Purchase #2	$158.32	4.788%	$165.9004	$165.90	$165.90	$165.90
Purchase #3	$43.57	13.213%	$49.3269	$49.33	$49.35	$49.30
Purchase #4	$159.91	8.770%	$173.9341	$173.93	$173.95	$173.90
Purchase #5	$191.69	11.748%	$214.2097	$214.21	$214.20	$214.20
Purchase #6	$31.56	11.604%	$35.2222	$35.22	$35.20	$35.20
Purchase #7	$45.35	4.798%	$47.5259	$47.53	$47.55	$47.50
7 purchase totals =	$795.72		$870.3221	$870.32	$870.35	$870.20