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	$39.79	8.280%	$43.0846	$43.08	$43.10	$43.10
Purchase #2	$24.86	11.294%	$27.6677	$27.67	$27.65	$27.70
Purchase #3	$70.29	11.414%	$78.3129	$78.31	$78.30	$78.30
Purchase #4	$36.72	10.121%	$40.4364	$40.44	$40.45	$40.40
Purchase #5	$47.97	7.336%	$51.4891	$51.49	$51.50	$51.50
Purchase #6	$117.58	3.689%	$121.9175	$121.92	$121.90	$121.90
Purchase #7	$232.72	9.627%	$255.124	$255.12	$255.10	$255.10
7 purchase totals =	$569.93		$618.0322	$618.03	$618.00	$618.00