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	$127.70	10.386%	$140.9629	$140.96	$140.95	$141.00
Purchase #2	$61.95	12.641%	$69.7811	$69.78	$69.80	$69.80
Purchase #3	$33.55	11.846%	$37.5243	$37.52	$37.50	$37.50
Purchase #4	$158.95	8.860%	$173.033	$173.03	$173.05	$173.00
Purchase #5	$39.71	13.542%	$45.0875	$45.09	$45.10	$45.10
Purchase #6	$72.52	12.511%	$81.593	$81.59	$81.60	$81.60
Purchase #7	$29.81	5.373%	$31.4117	$31.41	$31.40	$31.40
7 purchase totals =	$524.19		$579.3935	$579.38	$579.40	$579.40