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	$148.76	12.355%	$167.1393	$167.14	$167.15	$167.10
Purchase #2	$56.35	9.754%	$61.8464	$61.85	$61.85	$61.80
Purchase #3	$21.42	10.609%	$23.6924	$23.69	$23.70	$23.70
Purchase #4	$81.51	10.824%	$90.3326	$90.33	$90.35	$90.30
Purchase #5	$76.39	13.515%	$86.7141	$86.71	$86.70	$86.70
Purchase #6	$46.41	4.786%	$48.6312	$48.63	$48.65	$48.60
Purchase #7	$133.54	3.210%	$137.8266	$137.83	$137.85	$137.80
7 purchase totals =	$564.38		$616.1826	$616.18	$616.25	$616.00