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	$111.61	9.299%	$121.9886	$121.99	$122.00	$122.00
Purchase #2	$205.75	11.504%	$229.4195	$229.42	$229.40	$229.40
Purchase #3	$116.49	9.188%	$127.1931	$127.19	$127.20	$127.20
Purchase #4	$40.48	12.554%	$45.5619	$45.56	$45.55	$45.60
Purchase #5	$191.81	11.327%	$213.5363	$213.54	$213.55	$213.50
Purchase #6	$19.45	12.232%	$21.8291	$21.83	$21.85	$21.80
Purchase #7	$106.89	5.772%	$113.0597	$113.06	$113.05	$113.10
7 purchase totals =	$792.48		$872.5882	$872.59	$872.60	$872.60