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	$152.36	8.589%	$165.4462	$165.45	$165.45	$165.40
Purchase #2	$80.71	12.547%	$90.8367	$90.84	$90.85	$90.80
Purchase #3	$81.28	13.698%	$92.4137	$92.41	$92.40	$92.40
Purchase #4	$11.39	13.233%	$12.8972	$12.90	$12.90	$12.90
Purchase #5	$99.76	11.779%	$111.5107	$111.51	$111.50	$111.50
Purchase #6	$219.76	10.666%	$243.1996	$243.20	$243.20	$243.20
Purchase #7	$222.28	8.159%	$240.4158	$240.42	$240.40	$240.40
7 purchase totals =	$867.54		$956.7199	$956.73	$956.70	$956.60