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	$84.39	8.660%	$91.6982	$91.70	$91.70	$91.70
Purchase #2	$56.40	10.463%	$62.3011	$62.30	$62.30	$62.30
Purchase #3	$234.47	8.202%	$253.7012	$253.70	$253.70	$253.70
Purchase #4	$100.81	4.611%	$105.4583	$105.46	$105.45	$105.50
Purchase #5	$77.59	9.650%	$85.0774	$85.08	$85.10	$85.10
Purchase #6	$52.73	12.490%	$59.316	$59.32	$59.30	$59.30
Purchase #7	$114.96	10.549%	$127.0871	$127.09	$127.10	$127.10
7 purchase totals =	$721.35		$784.6393	$784.65	$784.65	$784.70