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	$133.99	5.704%	$141.6328	$141.63	$141.65	$141.60
Purchase #2	$142.85	5.434%	$150.6125	$150.61	$150.60	$150.60
Purchase #3	$137.32	8.234%	$148.6269	$148.63	$148.65	$148.60
Purchase #4	$153.45	10.670%	$169.8231	$169.82	$169.80	$169.80
Purchase #5	$140.51	8.828%	$152.9142	$152.91	$152.90	$152.90
Purchase #6	$90.84	10.361%	$100.2519	$100.25	$100.25	$100.30
Purchase #7	$115.77	12.157%	$129.8442	$129.84	$129.85	$129.80
7 purchase totals =	$914.73		$993.7056	$993.69	$993.70	$993.60