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	$90.83	13.823%	$103.3854	$103.39	$103.40	$103.40
Purchase #2	$191.54	11.737%	$214.021	$214.02	$214.00	$214.00
Purchase #3	$121.72	12.510%	$136.9472	$136.95	$136.95	$136.90
Purchase #4	$118.58	11.446%	$132.1527	$132.15	$132.15	$132.20
Purchase #5	$82.31	5.515%	$86.8494	$86.85	$86.85	$86.80
Purchase #6	$102.80	11.428%	$114.548	$114.55	$114.55	$114.50
Purchase #7	$28.49	13.443%	$32.3199	$32.32	$32.30	$32.30
7 purchase totals =	$736.27		$820.2236	$820.23	$820.20	$820.10