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	$89.36	11.108%	$99.2861	$99.29	$99.30	$99.30
Purchase #2	$128.40	8.762%	$139.6504	$139.65	$139.65	$139.70
Purchase #3	$151.47	6.638%	$161.5246	$161.52	$161.50	$161.50
Purchase #4	$128.73	5.758%	$136.1423	$136.14	$136.15	$136.10
Purchase #5	$30.29	11.522%	$33.78	$33.78	$33.80	$33.80
Purchase #6	$92.39	5.453%	$97.428	$97.43	$97.45	$97.40
Purchase #7	$16.45	13.232%	$18.6267	$18.63	$18.65	$18.60
7 purchase totals =	$637.09		$686.4381	$686.44	$686.50	$686.40