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	$32.50	10.110%	$35.7858	$35.79	$35.80	$35.80
Purchase #2	$146.36	13.814%	$166.5782	$166.58	$166.60	$166.60
Purchase #3	$58.92	13.752%	$67.0227	$67.02	$67.00	$67.00
Purchase #4	$145.36	11.684%	$162.3439	$162.34	$162.35	$162.30
Purchase #5	$38.96	10.873%	$43.1961	$43.20	$43.20	$43.20
Purchase #6	$99.81	3.837%	$103.6397	$103.64	$103.65	$103.60
Purchase #7	$161.73	10.412%	$178.5693	$178.57	$178.55	$178.60
7 purchase totals =	$683.64		$757.1357	$757.14	$757.15	$757.10