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	$39.66	4.567%	$41.4713	$41.47	$41.45	$41.50
Purchase #2	$103.34	13.548%	$117.3405	$117.34	$117.35	$117.30
Purchase #3	$159.50	6.334%	$169.6027	$169.60	$169.60	$169.60
Purchase #4	$221.65	11.114%	$246.2842	$246.28	$246.30	$246.30
Purchase #5	$51.97	13.685%	$59.0821	$59.08	$59.10	$59.10
Purchase #6	$127.51	9.196%	$139.2358	$139.24	$139.25	$139.20
Purchase #7	$96.81	13.550%	$109.9278	$109.93	$109.95	$109.90
7 purchase totals =	$800.44		$882.9444	$882.94	$883.00	$882.90