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	$49.90	13.171%	$56.4723	$56.47	$56.45	$56.50
Purchase #2	$111.91	7.172%	$119.9362	$119.94	$119.95	$119.90
Purchase #3	$113.56	13.385%	$128.76	$128.76	$128.75	$128.80
Purchase #4	$191.61	9.466%	$209.7478	$209.75	$209.75	$209.70
Purchase #5	$188.85	11.479%	$210.5281	$210.53	$210.55	$210.50
Purchase #6	$107.38	12.812%	$121.1375	$121.14	$121.15	$121.10
Purchase #7	$106.36	4.770%	$111.4334	$111.43	$111.45	$111.40
7 purchase totals =	$869.57		$958.0153	$958.02	$958.05	$957.90