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	$59.89	5.634%	$63.2642	$63.26	$63.25	$63.30
Purchase #2	$215.45	4.537%	$225.225	$225.23	$225.25	$225.20
Purchase #3	$114.68	7.404%	$123.1709	$123.17	$123.15	$123.20
Purchase #4	$53.84	11.134%	$59.8345	$59.83	$59.85	$59.80
Purchase #5	$70.49	10.704%	$78.0352	$78.04	$78.05	$78.00
Purchase #6	$7.83	7.841%	$8.444	$8.44	$8.45	$8.40
Purchase #7	$30.79	6.463%	$32.78	$32.78	$32.80	$32.80
7 purchase totals =	$552.97		$590.7538	$590.75	$590.80	$590.70