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	$17.94	4.196%	$18.6928	$18.69	$18.70	$18.70
Purchase #2	$72.73	11.293%	$80.9434	$80.94	$80.95	$80.90
Purchase #3	$81.63	11.406%	$90.9407	$90.94	$90.95	$90.90
Purchase #4	$209.67	9.725%	$230.0604	$230.06	$230.05	$230.10
Purchase #5	$77.83	9.614%	$85.3126	$85.31	$85.30	$85.30
Purchase #6	$38.47	13.367%	$43.6123	$43.61	$43.60	$43.60
Purchase #7	$147.95	10.201%	$163.0424	$163.04	$163.05	$163.00
7 purchase totals =	$646.22		$712.6046	$712.59	$712.60	$712.50