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	$99.38	6.819%	$106.1567	$106.16	$106.15	$106.20
Purchase #2	$150.95	9.538%	$165.3476	$165.35	$165.35	$165.30
Purchase #3	$108.35	4.135%	$112.8303	$112.83	$112.85	$112.80
Purchase #4	$198.40	11.606%	$221.4263	$221.43	$221.45	$221.40
Purchase #5	$197.33	9.448%	$215.9737	$215.97	$215.95	$216.00
Purchase #6	$90.75	9.137%	$99.0418	$99.04	$99.05	$99.00
Purchase #7	$19.26	11.648%	$21.5034	$21.50	$21.50	$21.50
7 purchase totals =	$864.42		$942.2798	$942.28	$942.30	$942.20