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	$135.78	11.594%	$151.5223	$151.52	$151.50	$151.50
Purchase #2	$127.99	8.222%	$138.5133	$138.51	$138.50	$138.50
Purchase #3	$62.71	6.223%	$66.6124	$66.61	$66.60	$66.60
Purchase #4	$80.69	4.576%	$84.3824	$84.38	$84.40	$84.40
Purchase #5	$6.90	13.280%	$7.8163	$7.82	$7.80	$7.80
Purchase #6	$47.64	11.602%	$53.1672	$53.17	$53.15	$53.20
Purchase #7	$58.98	13.809%	$67.1245	$67.12	$67.10	$67.10
7 purchase totals =	$520.69		$569.1384	$569.13	$569.05	$569.10