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	$36.48	6.190%	$38.7381	$38.74	$38.75	$38.70
Purchase #2	$71.56	3.870%	$74.3294	$74.33	$74.35	$74.30
Purchase #3	$100.63	4.836%	$105.4965	$105.50	$105.50	$105.50
Purchase #4	$158.71	5.155%	$166.8915	$166.89	$166.90	$166.90
Purchase #5	$192.59	6.836%	$205.7555	$205.76	$205.75	$205.80
Purchase #6	$145.54	7.262%	$156.1091	$156.11	$156.10	$156.10
Purchase #7	$70.38	6.208%	$74.7492	$74.75	$74.75	$74.70
7 purchase totals =	$775.89		$822.0693	$822.08	$822.10	$822.00