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	$237.26	7.871%	$255.9347	$255.93	$255.95	$255.90
Purchase #2	$141.80	3.178%	$146.3064	$146.31	$146.30	$146.30
Purchase #3	$109.64	7.656%	$118.034	$118.03	$118.05	$118.00
Purchase #4	$5.87	13.265%	$6.6487	$6.65	$6.65	$6.60
Purchase #5	$25.58	11.834%	$28.6071	$28.61	$28.60	$28.60
Purchase #6	$87.79	5.507%	$92.6246	$92.62	$92.60	$92.60
Purchase #7	$95.83	3.789%	$99.461	$99.46	$99.45	$99.50
7 purchase totals =	$703.77		$747.6165	$747.61	$747.60	$747.50