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	$107.42	8.479%	$116.5281	$116.53	$116.55	$116.50
Purchase #2	$90.71	12.605%	$102.144	$102.14	$102.15	$102.10
Purchase #3	$33.32	6.399%	$35.4521	$35.45	$35.45	$35.50
Purchase #4	$172.60	7.714%	$185.9144	$185.91	$185.90	$185.90
Purchase #5	$59.31	4.260%	$61.8366	$61.84	$61.85	$61.80
Purchase #6	$172.31	8.162%	$186.3739	$186.37	$186.35	$186.40
Purchase #7	$94.74	8.364%	$102.6641	$102.66	$102.65	$102.70
7 purchase totals =	$730.41		$790.9132	$790.90	$790.90	$790.90