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	$103.48	8.118%	$111.8805	$111.88	$111.90	$111.90
Purchase #2	$34.90	13.839%	$39.7298	$39.73	$39.75	$39.70
Purchase #3	$27.81	13.672%	$31.6122	$31.61	$31.60	$31.60
Purchase #4	$115.51	13.691%	$131.3245	$131.32	$131.30	$131.30
Purchase #5	$120.79	4.132%	$125.781	$125.78	$125.80	$125.80
Purchase #6	$113.80	9.768%	$124.916	$124.92	$124.90	$124.90
Purchase #7	$62.77	7.385%	$67.4056	$67.41	$67.40	$67.40
7 purchase totals =	$579.06		$632.6496	$632.65	$632.65	$632.60