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	$90.42	11.549%	$100.8626	$100.86	$100.85	$100.90
Purchase #2	$132.33	7.248%	$141.9213	$141.92	$141.90	$141.90
Purchase #3	$43.28	4.137%	$45.0705	$45.07	$45.05	$45.10
Purchase #4	$213.47	6.191%	$226.6859	$226.69	$226.70	$226.70
Purchase #5	$192.96	6.482%	$205.4677	$205.47	$205.45	$205.50
Purchase #6	$26.68	4.636%	$27.9169	$27.92	$27.90	$27.90
Purchase #7	$54.45	10.616%	$60.2304	$60.23	$60.25	$60.20
7 purchase totals =	$753.59		$808.1553	$808.16	$808.10	$808.20