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	$238.30	8.429%	$258.3863	$258.39	$258.40	$258.40
Purchase #2	$164.35	11.555%	$183.3406	$183.34	$183.35	$183.30
Purchase #3	$200.31	12.552%	$225.4529	$225.45	$225.45	$225.50
Purchase #4	$88.61	4.421%	$92.5274	$92.53	$92.55	$92.50
Purchase #5	$75.85	3.645%	$78.6147	$78.61	$78.60	$78.60
Purchase #6	$47.98	9.531%	$52.553	$52.55	$52.55	$52.60
Purchase #7	$110.49	12.446%	$124.2416	$124.24	$124.25	$124.20
7 purchase totals =	$925.89		$1,015.1165	$1,015.11	$1,015.15	$1,015.10