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	$61.45	13.315%	$69.6321	$69.63	$69.65	$69.60
Purchase #2	$91.61	10.183%	$100.9386	$100.94	$100.95	$100.90
Purchase #3	$55.98	12.436%	$62.9417	$62.94	$62.95	$62.90
Purchase #4	$96.69	8.172%	$104.5915	$104.59	$104.60	$104.60
Purchase #5	$42.73	4.776%	$44.7708	$44.77	$44.75	$44.80
Purchase #6	$31.32	6.409%	$33.3273	$33.33	$33.35	$33.30
Purchase #7	$203.61	10.508%	$225.0053	$225.01	$225.00	$225.00
7 purchase totals =	$583.39		$641.2073	$641.21	$641.25	$641.10