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	$103.68	8.182%	$112.1631	$112.16	$112.15	$112.20
Purchase #2	$85.93	4.614%	$89.8948	$89.89	$89.90	$89.90
Purchase #3	$125.52	4.684%	$131.3994	$131.40	$131.40	$131.40
Purchase #4	$74.51	9.462%	$81.5601	$81.56	$81.55	$81.60
Purchase #5	$48.49	12.315%	$54.4615	$54.46	$54.45	$54.50
Purchase #6	$153.41	6.826%	$163.8818	$163.88	$163.90	$163.90
Purchase #7	$155.54	11.478%	$173.3929	$173.39	$173.40	$173.40
7 purchase totals =	$747.08		$806.7536	$806.74	$806.75	$806.90