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	$95.92	4.167%	$99.917	$99.92	$99.90	$99.90
Purchase #2	$96.71	8.163%	$104.6044	$104.60	$104.60	$104.60
Purchase #3	$74.71	10.285%	$82.3939	$82.39	$82.40	$82.40
Purchase #4	$81.66	6.168%	$86.6968	$86.70	$86.70	$86.70
Purchase #5	$27.98	11.220%	$31.1194	$31.12	$31.10	$31.10
Purchase #6	$157.97	12.120%	$177.116	$177.12	$177.10	$177.10
Purchase #7	$92.30	13.243%	$104.5233	$104.52	$104.50	$104.50
7 purchase totals =	$627.25		$686.3708	$686.37	$686.30	$686.30