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	$5.40	11.619%	$6.0274	$6.03	$6.05	$6.00
Purchase #2	$38.95	3.302%	$40.2361	$40.24	$40.25	$40.20
Purchase #3	$71.99	7.357%	$77.2863	$77.29	$77.30	$77.30
Purchase #4	$63.48	4.575%	$66.3842	$66.38	$66.40	$66.40
Purchase #5	$42.73	3.271%	$44.1277	$44.13	$44.15	$44.10
Purchase #6	$155.87	4.176%	$162.3791	$162.38	$162.40	$162.40
Purchase #7	$90.38	10.836%	$100.1736	$100.17	$100.15	$100.20
7 purchase totals =	$468.80		$496.6144	$496.62	$496.70	$496.60