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	$109.40	6.461%	$116.4683	$116.47	$116.45	$116.50
Purchase #2	$130.91	12.770%	$147.6272	$147.63	$147.65	$147.60
Purchase #3	$178.86	10.702%	$198.0016	$198.00	$198.00	$198.00
Purchase #4	$73.38	6.836%	$78.3963	$78.40	$78.40	$78.40
Purchase #5	$6.76	4.674%	$7.076	$7.08	$7.10	$7.10
Purchase #6	$35.46	10.398%	$39.1471	$39.15	$39.15	$39.10
Purchase #7	$5.26	11.225%	$5.8504	$5.85	$5.85	$5.90
7 purchase totals =	$540.03		$592.5669	$592.58	$592.60	$592.60