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	$19.43	7.790%	$20.9436	$20.94	$20.95	$20.90
Purchase #2	$132.91	8.697%	$144.4692	$144.47	$144.45	$144.50
Purchase #3	$204.49	8.841%	$222.569	$222.57	$222.55	$222.60
Purchase #4	$60.32	11.420%	$67.2085	$67.21	$67.20	$67.20
Purchase #5	$204.94	8.301%	$221.9521	$221.95	$221.95	$222.00
Purchase #6	$75.61	3.597%	$78.3297	$78.33	$78.35	$78.30
Purchase #7	$100.67	8.491%	$109.2179	$109.22	$109.20	$109.20
7 purchase totals =	$798.37		$864.6900	$864.69	$864.65	$864.70