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	$108.35	4.205%	$112.9061	$112.91	$112.90	$112.90
Purchase #2	$157.46	13.257%	$178.3345	$178.33	$178.35	$178.30
Purchase #3	$232.64	9.778%	$255.3875	$255.39	$255.40	$255.40
Purchase #4	$205.45	8.175%	$222.2455	$222.25	$222.25	$222.20
Purchase #5	$83.86	8.407%	$90.9101	$90.91	$90.90	$90.90
Purchase #6	$207.47	9.104%	$226.3581	$226.36	$226.35	$226.40
Purchase #7	$62.37	5.110%	$65.5571	$65.56	$65.55	$65.60
7 purchase totals =	$1,057.60		$1,151.6989	$1,151.71	$1,151.70	$1,151.70