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	$138.28	7.631%	$148.8321	$148.83	$148.85	$148.80
Purchase #2	$143.44	3.774%	$148.8534	$148.85	$148.85	$148.90
Purchase #3	$50.85	10.166%	$56.0194	$56.02	$56.00	$56.00
Purchase #4	$29.59	4.313%	$30.8662	$30.87	$30.85	$30.90
Purchase #5	$180.94	10.755%	$200.4001	$200.40	$200.40	$200.40
Purchase #6	$129.30	10.769%	$143.2243	$143.22	$143.20	$143.20
Purchase #7	$35.65	6.113%	$37.8293	$37.83	$37.85	$37.80
7 purchase totals =	$708.05		$766.0248	$766.02	$766.00	$766.00