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	$249.59	3.833%	$259.1568	$259.16	$259.15	$259.20
Purchase #2	$187.27	7.208%	$200.7684	$200.77	$200.75	$200.80
Purchase #3	$89.46	5.707%	$94.5655	$94.57	$94.55	$94.60
Purchase #4	$86.25	7.163%	$92.4281	$92.43	$92.45	$92.40
Purchase #5	$185.50	9.687%	$203.4694	$203.47	$203.45	$203.50
Purchase #6	$54.94	11.262%	$61.1273	$61.13	$61.15	$61.10
Purchase #7	$238.74	7.694%	$257.1087	$257.11	$257.10	$257.10
7 purchase totals =	$1,091.75		$1,168.6242	$1,168.64	$1,168.60	$1,168.70