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	$112.97	13.103%	$127.7725	$127.77	$127.75	$127.80
Purchase #2	$216.69	12.422%	$243.6072	$243.61	$243.60	$243.60
Purchase #3	$141.51	13.376%	$160.4384	$160.44	$160.45	$160.40
Purchase #4	$90.81	4.195%	$94.6195	$94.62	$94.60	$94.60
Purchase #5	$20.69	9.304%	$22.615	$22.62	$22.60	$22.60
Purchase #6	$49.98	9.138%	$54.5472	$54.55	$54.55	$54.50
Purchase #7	$105.94	7.837%	$114.2425	$114.24	$114.25	$114.20
7 purchase totals =	$738.59		$817.8423	$817.85	$817.80	$817.70