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	$19.73	8.760%	$21.4583	$21.46	$21.45	$21.50
Purchase #2	$13.36	11.773%	$14.9329	$14.93	$14.95	$14.90
Purchase #3	$215.53	6.648%	$229.8584	$229.86	$229.85	$229.90
Purchase #4	$249.56	12.451%	$280.6327	$280.63	$280.65	$280.60
Purchase #5	$111.74	4.280%	$116.5225	$116.52	$116.50	$116.50
Purchase #6	$166.34	10.505%	$183.814	$183.81	$183.80	$183.80
Purchase #7	$63.39	10.677%	$70.1582	$70.16	$70.15	$70.20
7 purchase totals =	$839.65		$917.3770	$917.37	$917.35	$917.40