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	$72.98	5.661%	$77.1114	$77.11	$77.10	$77.10
Purchase #2	$227.63	10.584%	$251.7224	$251.72	$251.70	$251.70
Purchase #3	$13.75	6.799%	$14.6849	$14.68	$14.70	$14.70
Purchase #4	$86.98	10.111%	$95.7745	$95.77	$95.75	$95.80
Purchase #5	$41.61	8.587%	$45.1831	$45.18	$45.20	$45.20
Purchase #6	$6.82	4.589%	$7.133	$7.13	$7.15	$7.10
Purchase #7	$69.47	13.395%	$78.7755	$78.78	$78.80	$78.80
7 purchase totals =	$519.24		$570.3848	$570.37	$570.40	$570.40