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	$155.49	7.178%	$166.6511	$166.65	$166.65	$166.70
Purchase #2	$156.32	7.833%	$168.5645	$168.56	$168.55	$168.60
Purchase #3	$130.51	5.618%	$137.8421	$137.84	$137.85	$137.80
Purchase #4	$40.61	3.579%	$42.0634	$42.06	$42.05	$42.10
Purchase #5	$129.30	11.404%	$144.0454	$144.05	$144.05	$144.00
Purchase #6	$53.56	5.722%	$56.6247	$56.62	$56.60	$56.60
Purchase #7	$200.44	9.140%	$218.7602	$218.76	$218.75	$218.80
7 purchase totals =	$866.23		$934.5514	$934.54	$934.50	$934.60