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	$75.64	3.730%	$78.4614	$78.46	$78.45	$78.50
Purchase #2	$16.95	13.124%	$19.1745	$19.17	$19.15	$19.20
Purchase #3	$56.40	13.137%	$63.8093	$63.81	$63.80	$63.80
Purchase #4	$167.41	4.299%	$174.607	$174.61	$174.60	$174.60
Purchase #5	$104.77	3.491%	$108.4275	$108.43	$108.45	$108.40
Purchase #6	$130.73	12.791%	$147.4517	$147.45	$147.45	$147.50
Purchase #7	$50.92	8.605%	$55.3017	$55.30	$55.30	$55.30
7 purchase totals =	$602.82		$647.2331	$647.23	$647.20	$647.30