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	$92.49	4.335%	$96.4994	$96.50	$96.50	$96.50
Purchase #2	$245.28	10.817%	$271.8119	$271.81	$271.80	$271.80
Purchase #3	$133.70	10.693%	$147.9965	$148.00	$148.00	$148.00
Purchase #4	$124.34	3.614%	$128.8336	$128.83	$128.85	$128.80
Purchase #5	$38.59	6.665%	$41.162	$41.16	$41.15	$41.20
Purchase #6	$95.81	5.177%	$100.7701	$100.77	$100.75	$100.80
Purchase #7	$29.75	10.760%	$32.9511	$32.95	$32.95	$33.00
7 purchase totals =	$759.96		$820.0246	$820.02	$820.00	$820.10