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	$151.81	9.651%	$166.4612	$166.46	$166.45	$166.50
Purchase #2	$37.72	10.781%	$41.7866	$41.79	$41.80	$41.80
Purchase #3	$134.63	13.376%	$152.6381	$152.64	$152.65	$152.60
Purchase #4	$177.62	10.541%	$196.3429	$196.34	$196.35	$196.30
Purchase #5	$144.52	8.159%	$156.3114	$156.31	$156.30	$156.30
Purchase #6	$134.62	9.853%	$147.8841	$147.88	$147.90	$147.90
Purchase #7	$128.32	4.784%	$134.4588	$134.46	$134.45	$134.50
7 purchase totals =	$909.24		$995.8831	$995.88	$995.90	$995.90