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	$75.82	3.183%	$78.2334	$78.23	$78.25	$78.20
Purchase #2	$93.60	5.196%	$98.4635	$98.46	$98.45	$98.50
Purchase #3	$94.53	10.204%	$104.1758	$104.18	$104.20	$104.20
Purchase #4	$86.43	4.302%	$90.1482	$90.15	$90.15	$90.10
Purchase #5	$248.84	10.757%	$275.6077	$275.61	$275.60	$275.60
Purchase #6	$103.82	8.144%	$112.2751	$112.28	$112.30	$112.30
Purchase #7	$173.46	5.843%	$183.5953	$183.60	$183.60	$183.60
7 purchase totals =	$876.50		$942.4990	$942.51	$942.55	$942.50