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	$247.52	5.207%	$260.4084	$260.41	$260.40	$260.40
Purchase #2	$86.31	4.563%	$90.2483	$90.25	$90.25	$90.20
Purchase #3	$42.78	4.856%	$44.8574	$44.86	$44.85	$44.90
Purchase #4	$106.75	3.818%	$110.8257	$110.83	$110.85	$110.80
Purchase #5	$19.76	10.584%	$21.8514	$21.85	$21.85	$21.90
Purchase #6	$58.60	13.491%	$66.5057	$66.51	$66.50	$66.50
Purchase #7	$47.62	12.568%	$53.6049	$53.60	$53.60	$53.60
7 purchase totals =	$609.34		$648.3018	$648.31	$648.30	$648.30