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	$42.26	4.142%	$44.0104	$44.01	$44.00	$44.00
Purchase #2	$108.66	10.285%	$119.8357	$119.84	$119.85	$119.80
Purchase #3	$217.52	10.768%	$240.9426	$240.94	$240.95	$240.90
Purchase #4	$209.39	9.231%	$228.7188	$228.72	$228.70	$228.70
Purchase #5	$223.62	8.406%	$242.4175	$242.42	$242.40	$242.40
Purchase #6	$82.70	9.443%	$90.5094	$90.51	$90.50	$90.50
Purchase #7	$176.52	6.863%	$188.6346	$188.63	$188.65	$188.60
7 purchase totals =	$1,060.67		$1,155.0690	$1,155.07	$1,155.05	$1,154.90