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	$30.44	6.622%	$32.4557	$32.46	$32.45	$32.50
Purchase #2	$188.52	3.313%	$194.7657	$194.77	$194.75	$194.80
Purchase #3	$203.46	13.532%	$230.9922	$230.99	$231.00	$231.00
Purchase #4	$104.49	9.685%	$114.6099	$114.61	$114.60	$114.60
Purchase #5	$117.57	8.842%	$127.9655	$127.97	$127.95	$128.00
Purchase #6	$151.54	11.251%	$168.5898	$168.59	$168.60	$168.60
Purchase #7	$95.94	7.814%	$103.4368	$103.44	$103.45	$103.40
7 purchase totals =	$891.96		$972.8156	$972.83	$972.80	$972.90