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	$54.35	11.501%	$60.6008	$60.60	$60.60	$60.60
Purchase #2	$62.72	13.395%	$71.1213	$71.12	$71.10	$71.10
Purchase #3	$211.65	12.470%	$238.0428	$238.04	$238.05	$238.00
Purchase #4	$87.50	13.397%	$99.2224	$99.22	$99.20	$99.20
Purchase #5	$156.53	4.798%	$164.0403	$164.04	$164.05	$164.00
Purchase #6	$123.72	4.349%	$129.1006	$129.10	$129.10	$129.10
Purchase #7	$86.76	5.448%	$91.4867	$91.49	$91.50	$91.50
7 purchase totals =	$783.23		$853.6149	$853.61	$853.60	$853.50