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	$248.67	8.483%	$269.7647	$269.76	$269.75	$269.80
Purchase #2	$242.53	4.164%	$252.6289	$252.63	$252.65	$252.60
Purchase #3	$172.75	6.429%	$183.8561	$183.86	$183.85	$183.90
Purchase #4	$81.76	9.312%	$89.3735	$89.37	$89.35	$89.40
Purchase #5	$115.89	13.121%	$131.0959	$131.10	$131.10	$131.10
Purchase #6	$223.96	13.146%	$253.4018	$253.40	$253.40	$253.40
Purchase #7	$14.80	11.572%	$16.5127	$16.51	$16.50	$16.50
7 purchase totals =	$1,100.36		$1,196.6336	$1,196.63	$1,196.60	$1,196.70