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	$136.49	8.646%	$148.2909	$148.29	$148.30	$148.30
Purchase #2	$54.91	11.698%	$61.3334	$61.33	$61.35	$61.30
Purchase #3	$175.48	13.839%	$199.7647	$199.76	$199.75	$199.80
Purchase #4	$152.26	10.700%	$168.5518	$168.55	$168.55	$168.60
Purchase #5	$151.69	5.669%	$160.2893	$160.29	$160.30	$160.30
Purchase #6	$65.68	3.629%	$68.0635	$68.06	$68.05	$68.10
Purchase #7	$80.72	12.220%	$90.584	$90.58	$90.60	$90.60
7 purchase totals =	$817.23		$896.8776	$896.86	$896.90	$897.00