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	$25.43	10.340%	$28.0595	$28.06	$28.05	$28.10
Purchase #2	$72.50	7.740%	$78.1115	$78.11	$78.10	$78.10
Purchase #3	$88.28	9.618%	$96.7708	$96.77	$96.75	$96.80
Purchase #4	$117.93	10.357%	$130.144	$130.14	$130.15	$130.10
Purchase #5	$153.50	11.209%	$170.7058	$170.71	$170.70	$170.70
Purchase #6	$170.54	9.797%	$187.2478	$187.25	$187.25	$187.20
Purchase #7	$62.32	5.275%	$65.6074	$65.61	$65.60	$65.60
7 purchase totals =	$690.50		$756.6468	$756.65	$756.60	$756.60