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	$72.44	10.149%	$79.7919	$79.79	$79.80	$79.80
Purchase #2	$51.70	11.186%	$57.4832	$57.48	$57.50	$57.50
Purchase #3	$55.35	11.701%	$61.8265	$61.83	$61.85	$61.80
Purchase #4	$79.32	12.176%	$88.978	$88.98	$89.00	$89.00
Purchase #5	$12.95	3.162%	$13.3595	$13.36	$13.35	$13.40
Purchase #6	$138.33	7.201%	$148.2911	$148.29	$148.30	$148.30
Purchase #7	$132.31	7.722%	$142.527	$142.53	$142.55	$142.50
7 purchase totals =	$542.40		$592.2572	$592.26	$592.35	$592.30