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	$76.89	3.190%	$79.3428	$79.34	$79.35	$79.30
Purchase #2	$136.73	8.378%	$148.1852	$148.19	$148.20	$148.20
Purchase #3	$85.27	6.256%	$90.6045	$90.60	$90.60	$90.60
Purchase #4	$150.66	4.410%	$157.3041	$157.30	$157.30	$157.30
Purchase #5	$136.90	8.475%	$148.5023	$148.50	$148.50	$148.50
Purchase #6	$41.58	7.269%	$44.6025	$44.60	$44.60	$44.60
Purchase #7	$40.65	12.791%	$45.8495	$45.85	$45.85	$45.80
7 purchase totals =	$668.68		$714.3909	$714.38	$714.40	$714.30