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	$19.37	4.873%	$20.3139	$20.31	$20.30	$20.30
Purchase #2	$52.54	13.848%	$59.8157	$59.82	$59.80	$59.80
Purchase #3	$127.75	7.380%	$137.178	$137.18	$137.20	$137.20
Purchase #4	$243.98	13.438%	$276.766	$276.77	$276.75	$276.80
Purchase #5	$172.96	7.223%	$185.4529	$185.45	$185.45	$185.50
Purchase #6	$160.41	4.348%	$167.3846	$167.38	$167.40	$167.40
Purchase #7	$30.62	12.789%	$34.536	$34.54	$34.55	$34.50
7 purchase totals =	$807.63		$881.4471	$881.45	$881.45	$881.50