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	$81.27	11.692%	$90.7721	$90.77	$90.75	$90.80
Purchase #2	$112.85	9.208%	$123.2412	$123.24	$123.25	$123.20
Purchase #3	$103.82	6.666%	$110.7406	$110.74	$110.75	$110.70
Purchase #4	$72.75	11.636%	$81.2152	$81.22	$81.20	$81.20
Purchase #5	$186.48	4.553%	$194.9704	$194.97	$194.95	$195.00
Purchase #6	$233.98	8.382%	$253.5922	$253.59	$253.60	$253.60
Purchase #7	$40.73	13.793%	$46.3479	$46.35	$46.35	$46.30
7 purchase totals =	$831.88		$900.8796	$900.88	$900.85	$900.80