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	$125.96	5.169%	$132.4709	$132.47	$132.45	$132.50
Purchase #2	$243.31	4.645%	$254.6117	$254.61	$254.60	$254.60
Purchase #3	$81.77	6.180%	$86.8234	$86.82	$86.80	$86.80
Purchase #4	$211.89	5.777%	$224.1309	$224.13	$224.15	$224.10
Purchase #5	$175.32	7.367%	$188.2358	$188.24	$188.25	$188.20
Purchase #6	$58.60	13.550%	$66.5403	$66.54	$66.55	$66.50
Purchase #7	$121.42	12.709%	$136.8513	$136.85	$136.85	$136.90
7 purchase totals =	$1,018.27		$1,089.6643	$1,089.66	$1,089.65	$1,089.60