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	$56.51	5.329%	$59.5214	$59.52	$59.50	$59.50
Purchase #2	$210.55	8.493%	$228.432	$228.43	$228.45	$228.40
Purchase #3	$229.72	8.453%	$249.1382	$249.14	$249.15	$249.10
Purchase #4	$7.85	3.617%	$8.1339	$8.13	$8.15	$8.10
Purchase #5	$108.63	8.143%	$117.4757	$117.48	$117.50	$117.50
Purchase #6	$89.98	11.192%	$100.0506	$100.05	$100.05	$100.10
Purchase #7	$81.38	6.619%	$86.7665	$86.77	$86.75	$86.80
7 purchase totals =	$784.62		$849.5183	$849.52	$849.55	$849.50