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	$7.51	6.346%	$7.9866	$7.99	$8.00	$8.00
Purchase #2	$70.59	5.402%	$74.4033	$74.40	$74.40	$74.40
Purchase #3	$139.97	7.816%	$150.9101	$150.91	$150.90	$150.90
Purchase #4	$212.82	4.551%	$222.5054	$222.51	$222.50	$222.50
Purchase #5	$60.95	11.112%	$67.7228	$67.72	$67.70	$67.70
Purchase #6	$161.25	8.270%	$174.5854	$174.59	$174.60	$174.60
Purchase #7	$119.89	3.382%	$123.9447	$123.94	$123.95	$123.90
7 purchase totals =	$772.98		$822.0583	$822.06	$822.05	$822.00