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	$51.90	6.762%	$55.4095	$55.41	$55.40	$55.40
Purchase #2	$142.89	6.566%	$152.2722	$152.27	$152.25	$152.30
Purchase #3	$172.59	5.138%	$181.4577	$181.46	$181.45	$181.50
Purchase #4	$111.84	4.513%	$116.8873	$116.89	$116.90	$116.90
Purchase #5	$109.74	9.697%	$120.3815	$120.38	$120.40	$120.40
Purchase #6	$51.28	8.558%	$55.6685	$55.67	$55.65	$55.70
Purchase #7	$19.78	10.664%	$21.8893	$21.89	$21.90	$21.90
7 purchase totals =	$660.02		$703.9660	$703.97	$703.95	$704.10