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	$81.86	10.616%	$90.5503	$90.55	$90.55	$90.60
Purchase #2	$31.88	11.139%	$35.4311	$35.43	$35.45	$35.40
Purchase #3	$19.90	4.670%	$20.8293	$20.83	$20.85	$20.80
Purchase #4	$152.92	6.140%	$162.3093	$162.31	$162.30	$162.30
Purchase #5	$127.99	7.423%	$137.4907	$137.49	$137.50	$137.50
Purchase #6	$221.39	6.269%	$235.2689	$235.27	$235.25	$235.30
Purchase #7	$172.50	11.724%	$192.7239	$192.72	$192.70	$192.70
7 purchase totals =	$808.44		$874.6035	$874.60	$874.60	$874.60