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	$80.84	11.874%	$90.4389	$90.44	$90.45	$90.40
Purchase #2	$232.29	13.702%	$264.1184	$264.12	$264.10	$264.10
Purchase #3	$13.80	10.446%	$15.2415	$15.24	$15.25	$15.20
Purchase #4	$44.59	8.784%	$48.5068	$48.51	$48.50	$48.50
Purchase #5	$164.48	12.623%	$185.2423	$185.24	$185.25	$185.20
Purchase #6	$149.43	5.339%	$157.4081	$157.41	$157.40	$157.40
Purchase #7	$162.45	3.795%	$168.615	$168.62	$168.60	$168.60
7 purchase totals =	$847.88		$929.5710	$929.58	$929.55	$929.40