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	$69.78	12.351%	$78.3985	$78.40	$78.40	$78.40
Purchase #2	$60.65	4.445%	$63.3459	$63.35	$63.35	$63.30
Purchase #3	$184.67	10.837%	$204.6827	$204.68	$204.70	$204.70
Purchase #4	$95.54	8.874%	$104.0182	$104.02	$104.00	$104.00
Purchase #5	$84.27	5.855%	$89.204	$89.20	$89.20	$89.20
Purchase #6	$140.71	11.558%	$156.9733	$156.97	$156.95	$157.00
Purchase #7	$106.69	4.514%	$111.506	$111.51	$111.50	$111.50
7 purchase totals =	$742.31		$808.1286	$808.13	$808.10	$808.10