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	$192.61	9.264%	$210.4534	$210.45	$210.45	$210.50
Purchase #2	$95.45	5.150%	$100.3657	$100.37	$100.35	$100.40
Purchase #3	$33.54	11.262%	$37.3173	$37.32	$37.30	$37.30
Purchase #4	$101.66	6.847%	$108.6207	$108.62	$108.60	$108.60
Purchase #5	$95.29	7.426%	$102.3662	$102.37	$102.35	$102.40
Purchase #6	$13.27	9.873%	$14.5801	$14.58	$14.60	$14.60
Purchase #7	$88.95	10.238%	$98.0567	$98.06	$98.05	$98.10
7 purchase totals =	$620.77		$671.7601	$671.77	$671.70	$671.90