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	$77.86	5.684%	$82.2856	$82.29	$82.30	$82.30
Purchase #2	$189.72	7.615%	$204.1672	$204.17	$204.15	$204.20
Purchase #3	$165.51	9.685%	$181.5396	$181.54	$181.55	$181.50
Purchase #4	$50.35	13.699%	$57.2474	$57.25	$57.25	$57.20
Purchase #5	$183.70	13.284%	$208.1027	$208.10	$208.10	$208.10
Purchase #6	$89.82	9.411%	$98.273	$98.27	$98.25	$98.30
Purchase #7	$140.71	12.565%	$158.3902	$158.39	$158.40	$158.40
7 purchase totals =	$897.67		$990.0057	$990.01	$990.00	$990.00