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	$156.45	12.210%	$175.5525	$175.55	$175.55	$175.60
Purchase #2	$156.67	10.798%	$173.5872	$173.59	$173.60	$173.60
Purchase #3	$53.58	10.328%	$59.1137	$59.11	$59.10	$59.10
Purchase #4	$238.96	9.624%	$261.9575	$261.96	$261.95	$262.00
Purchase #5	$139.38	4.402%	$145.5155	$145.52	$145.50	$145.50
Purchase #6	$54.48	8.408%	$59.0607	$59.06	$59.05	$59.10
Purchase #7	$93.43	12.213%	$104.8406	$104.84	$104.85	$104.80
7 purchase totals =	$892.95		$979.6277	$979.63	$979.60	$979.70