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	$110.58	5.381%	$116.5303	$116.53	$116.55	$116.50
Purchase #2	$135.91	11.748%	$151.8767	$151.88	$151.90	$151.90
Purchase #3	$167.80	7.631%	$180.6048	$180.60	$180.60	$180.60
Purchase #4	$55.86	10.820%	$61.9041	$61.90	$61.90	$61.90
Purchase #5	$164.46	11.171%	$182.8318	$182.83	$182.85	$182.80
Purchase #6	$180.42	8.857%	$196.3998	$196.40	$196.40	$196.40
Purchase #7	$27.27	8.686%	$29.6387	$29.64	$29.65	$29.60
7 purchase totals =	$842.30		$919.7862	$919.78	$919.85	$919.70