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	$81.89	5.370%	$86.2875	$86.29	$86.30	$86.30
Purchase #2	$41.78	11.204%	$46.461	$46.46	$46.45	$46.50
Purchase #3	$53.43	5.129%	$56.1704	$56.17	$56.15	$56.20
Purchase #4	$245.60	12.242%	$275.6664	$275.67	$275.65	$275.70
Purchase #5	$238.54	4.437%	$249.124	$249.12	$249.10	$249.10
Purchase #6	$109.95	12.407%	$123.5915	$123.59	$123.60	$123.60
Purchase #7	$214.82	8.532%	$233.1484	$233.15	$233.15	$233.10
7 purchase totals =	$986.01		$1,070.4492	$1,070.45	$1,070.40	$1,070.50