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	$73.79	5.138%	$77.5813	$77.58	$77.60	$77.60
Purchase #2	$80.62	13.333%	$91.3691	$91.37	$91.35	$91.40
Purchase #3	$157.98	11.856%	$176.7101	$176.71	$176.70	$176.70
Purchase #4	$53.38	12.274%	$59.9319	$59.93	$59.95	$59.90
Purchase #5	$108.45	3.159%	$111.8759	$111.88	$111.90	$111.90
Purchase #6	$218.74	12.560%	$246.2137	$246.21	$246.20	$246.20
Purchase #7	$73.83	7.519%	$79.3813	$79.38	$79.40	$79.40
7 purchase totals =	$766.79		$843.0633	$843.06	$843.10	$843.10