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	$44.54	6.230%	$47.3148	$47.31	$47.30	$47.30
Purchase #2	$21.74	12.131%	$24.3773	$24.38	$24.40	$24.40
Purchase #3	$58.55	6.103%	$62.1233	$62.12	$62.10	$62.10
Purchase #4	$108.37	12.184%	$121.5738	$121.57	$121.55	$121.60
Purchase #5	$176.98	10.781%	$196.0602	$196.06	$196.05	$196.10
Purchase #6	$131.54	9.142%	$143.5654	$143.57	$143.55	$143.60
Purchase #7	$60.58	7.716%	$65.2544	$65.25	$65.25	$65.30
7 purchase totals =	$602.30		$660.2692	$660.26	$660.20	$660.40