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	$236.54	4.423%	$247.0022	$247.00	$247.00	$247.00
Purchase #2	$222.55	13.776%	$253.2085	$253.21	$253.20	$253.20
Purchase #3	$94.54	4.302%	$98.6071	$98.61	$98.60	$98.60
Purchase #4	$145.96	6.627%	$155.6328	$155.63	$155.65	$155.60
Purchase #5	$128.84	10.369%	$142.1994	$142.20	$142.20	$142.20
Purchase #6	$103.59	7.834%	$111.7052	$111.71	$111.70	$111.70
Purchase #7	$209.39	6.392%	$222.7742	$222.77	$222.75	$222.80
7 purchase totals =	$1,141.41		$1,231.1294	$1,231.13	$1,231.10	$1,231.10