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	$103.44	10.133%	$113.9216	$113.92	$113.90	$113.90
Purchase #2	$202.27	11.195%	$224.9141	$224.91	$224.90	$224.90
Purchase #3	$72.92	8.123%	$78.8433	$78.84	$78.85	$78.80
Purchase #4	$37.39	10.259%	$41.2258	$41.23	$41.25	$41.20
Purchase #5	$91.77	8.193%	$99.2887	$99.29	$99.30	$99.30
Purchase #6	$90.38	6.156%	$95.9438	$95.94	$95.95	$95.90
Purchase #7	$242.32	8.322%	$262.4859	$262.49	$262.50	$262.50
7 purchase totals =	$840.49		$916.6232	$916.62	$916.65	$916.50