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	$72.92	13.540%	$82.7934	$82.79	$82.80	$82.80
Purchase #2	$102.42	5.204%	$107.7499	$107.75	$107.75	$107.70
Purchase #3	$146.27	13.740%	$166.3675	$166.37	$166.35	$166.40
Purchase #4	$38.75	12.408%	$43.5581	$43.56	$43.55	$43.60
Purchase #5	$37.68	4.258%	$39.2844	$39.28	$39.30	$39.30
Purchase #6	$29.75	9.117%	$32.4623	$32.46	$32.45	$32.50
Purchase #7	$28.49	11.453%	$31.753	$31.75	$31.75	$31.80
7 purchase totals =	$456.28		$503.9686	$503.96	$503.95	$504.10