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	$55.76	7.442%	$59.9097	$59.91	$59.90	$59.90
Purchase #2	$57.27	8.818%	$62.3201	$62.32	$62.30	$62.30
Purchase #3	$200.48	7.492%	$215.5	$215.50	$215.50	$215.50
Purchase #4	$249.95	10.273%	$275.6274	$275.63	$275.65	$275.60
Purchase #5	$110.32	7.743%	$118.8621	$118.86	$118.85	$118.90
Purchase #6	$16.57	5.707%	$17.5156	$17.52	$17.50	$17.50
Purchase #7	$107.46	8.646%	$116.751	$116.75	$116.75	$116.80
7 purchase totals =	$797.81		$866.4859	$866.49	$866.45	$866.50