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	$165.66	6.767%	$176.8702	$176.87	$176.85	$176.90
Purchase #2	$25.79	11.236%	$28.6878	$28.69	$28.70	$28.70
Purchase #3	$145.59	9.402%	$159.2784	$159.28	$159.30	$159.30
Purchase #4	$164.56	8.693%	$178.8652	$178.87	$178.85	$178.90
Purchase #5	$130.28	12.146%	$146.1038	$146.10	$146.10	$146.10
Purchase #6	$68.59	3.528%	$71.0099	$71.01	$71.00	$71.00
Purchase #7	$163.75	9.448%	$179.2211	$179.22	$179.20	$179.20
7 purchase totals =	$864.22		$940.0364	$940.04	$940.00	$940.10