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	$40.46	8.357%	$43.8412	$43.84	$43.85	$43.80
Purchase #2	$82.28	8.103%	$88.9471	$88.95	$88.95	$88.90
Purchase #3	$67.77	3.372%	$70.0552	$70.06	$70.05	$70.10
Purchase #4	$206.51	6.365%	$219.6544	$219.65	$219.65	$219.70
Purchase #5	$12.38	10.824%	$13.72	$13.72	$13.70	$13.70
Purchase #6	$80.49	12.138%	$90.2599	$90.26	$90.25	$90.30
Purchase #7	$123.91	8.184%	$134.0508	$134.05	$134.05	$134.10
7 purchase totals =	$613.80		$660.5286	$660.53	$660.50	$660.60