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	$54.63	4.327%	$56.9938	$56.99	$57.00	$57.00
Purchase #2	$105.85	12.470%	$119.0495	$119.05	$119.05	$119.00
Purchase #3	$96.35	3.193%	$99.4265	$99.43	$99.45	$99.40
Purchase #4	$141.65	10.342%	$156.2994	$156.30	$156.30	$156.30
Purchase #5	$175.37	6.661%	$187.0514	$187.05	$187.05	$187.10
Purchase #6	$103.49	8.171%	$111.9462	$111.95	$111.95	$111.90
Purchase #7	$210.72	12.557%	$237.1801	$237.18	$237.20	$237.20
7 purchase totals =	$888.06		$967.9469	$967.95	$968.00	$967.90