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	$103.41	6.405%	$110.0334	$110.03	$110.05	$110.00
Purchase #2	$62.40	5.485%	$65.8226	$65.82	$65.80	$65.80
Purchase #3	$79.79	12.844%	$90.0382	$90.04	$90.05	$90.00
Purchase #4	$237.45	11.505%	$264.7686	$264.77	$264.75	$264.80
Purchase #5	$5.38	10.603%	$5.9504	$5.95	$5.95	$6.00
Purchase #6	$75.82	9.301%	$82.872	$82.87	$82.85	$82.90
Purchase #7	$167.83	11.581%	$187.2664	$187.27	$187.25	$187.30
7 purchase totals =	$732.08		$806.7516	$806.75	$806.70	$806.80