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	$55.89	8.543%	$60.6647	$60.66	$60.65	$60.70
Purchase #2	$67.80	10.110%	$74.6546	$74.65	$74.65	$74.70
Purchase #3	$59.28	5.747%	$62.6868	$62.69	$62.70	$62.70
Purchase #4	$111.61	10.477%	$123.3034	$123.30	$123.30	$123.30
Purchase #5	$78.65	12.699%	$88.6378	$88.64	$88.65	$88.60
Purchase #6	$39.97	6.409%	$42.5317	$42.53	$42.55	$42.50
Purchase #7	$78.39	5.189%	$82.4577	$82.46	$82.45	$82.50
7 purchase totals =	$491.59		$534.9367	$534.93	$534.95	$535.00