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	$19.50	3.697%	$20.2209	$20.22	$20.20	$20.20
Purchase #2	$173.60	13.314%	$196.7131	$196.71	$196.70	$196.70
Purchase #3	$12.78	4.373%	$13.3389	$13.34	$13.35	$13.30
Purchase #4	$11.69	13.627%	$13.283	$13.28	$13.30	$13.30
Purchase #5	$186.96	10.617%	$206.8095	$206.81	$206.80	$206.80
Purchase #6	$101.25	4.434%	$105.7394	$105.74	$105.75	$105.70
Purchase #7	$52.64	7.221%	$56.4411	$56.44	$56.45	$56.40
7 purchase totals =	$558.42		$612.5459	$612.54	$612.55	$612.40