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	$81.89	9.266%	$89.4779	$89.48	$89.50	$89.50
Purchase #2	$143.85	10.800%	$159.3858	$159.39	$159.40	$159.40
Purchase #3	$49.67	7.283%	$53.2875	$53.29	$53.30	$53.30
Purchase #4	$182.59	6.800%	$195.0061	$195.01	$195.00	$195.00
Purchase #5	$155.52	7.574%	$167.2991	$167.30	$167.30	$167.30
Purchase #6	$52.65	8.144%	$56.9378	$56.94	$56.95	$56.90
Purchase #7	$34.92	11.865%	$39.0633	$39.06	$39.05	$39.10
7 purchase totals =	$701.09		$760.4575	$760.47	$760.50	$760.50