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	$122.61	7.590%	$131.9161	$131.92	$131.90	$131.90
Purchase #2	$162.32	10.717%	$179.7158	$179.72	$179.70	$179.70
Purchase #3	$155.32	5.405%	$163.715	$163.72	$163.70	$163.70
Purchase #4	$105.98	3.717%	$109.9193	$109.92	$109.90	$109.90
Purchase #5	$115.63	4.237%	$120.5292	$120.53	$120.55	$120.50
Purchase #6	$49.93	5.307%	$52.5798	$52.58	$52.60	$52.60
Purchase #7	$82.40	10.284%	$90.874	$90.87	$90.85	$90.90
7 purchase totals =	$794.19		$849.2492	$849.26	$849.20	$849.20