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	$50.41	3.703%	$52.2767	$52.28	$52.30	$52.30
Purchase #2	$166.58	13.256%	$188.6618	$188.66	$188.65	$188.70
Purchase #3	$118.28	11.236%	$131.5699	$131.57	$131.55	$131.60
Purchase #4	$44.26	9.637%	$48.5253	$48.53	$48.55	$48.50
Purchase #5	$52.71	12.314%	$59.2007	$59.20	$59.20	$59.20
Purchase #6	$34.74	12.429%	$39.0578	$39.06	$39.05	$39.10
Purchase #7	$139.31	13.771%	$158.4944	$158.49	$158.50	$158.50
7 purchase totals =	$606.29		$677.7866	$677.79	$677.80	$677.90