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	$112.61	10.193%	$124.0883	$124.09	$124.10	$124.10
Purchase #2	$78.54	13.826%	$89.3989	$89.40	$89.40	$89.40
Purchase #3	$168.47	7.817%	$181.6393	$181.64	$181.65	$181.60
Purchase #4	$26.58	8.843%	$28.9305	$28.93	$28.95	$28.90
Purchase #5	$21.56	5.342%	$22.7117	$22.71	$22.70	$22.70
Purchase #6	$48.50	8.779%	$52.7578	$52.76	$52.75	$52.80
Purchase #7	$184.78	3.399%	$191.0607	$191.06	$191.05	$191.10
7 purchase totals =	$641.04		$690.5872	$690.59	$690.60	$690.60