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	$13.37	3.256%	$13.8053	$13.81	$13.80	$13.80
Purchase #2	$225.64	6.598%	$240.5277	$240.53	$240.55	$240.50
Purchase #3	$86.31	5.837%	$91.3479	$91.35	$91.35	$91.30
Purchase #4	$147.41	8.598%	$160.0843	$160.08	$160.10	$160.10
Purchase #5	$35.93	5.240%	$37.8127	$37.81	$37.80	$37.80
Purchase #6	$132.42	10.433%	$146.2354	$146.24	$146.25	$146.20
Purchase #7	$118.62	11.442%	$132.1925	$132.19	$132.20	$132.20
7 purchase totals =	$759.70		$822.0058	$822.01	$822.05	$821.90