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	$8.81	10.767%	$9.7586	$9.76	$9.75	$9.80
Purchase #2	$133.30	4.363%	$139.1159	$139.12	$139.10	$139.10
Purchase #3	$114.58	12.201%	$128.5599	$128.56	$128.55	$128.60
Purchase #4	$80.40	10.769%	$89.0583	$89.06	$89.05	$89.10
Purchase #5	$69.51	13.203%	$78.6874	$78.69	$78.70	$78.70
Purchase #6	$31.84	12.376%	$35.7805	$35.78	$35.80	$35.80
Purchase #7	$70.75	10.696%	$78.3174	$78.32	$78.30	$78.30
7 purchase totals =	$509.19		$559.2780	$559.29	$559.25	$559.40