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	$171.71	4.451%	$179.3528	$179.35	$179.35	$179.40
Purchase #2	$185.68	3.634%	$192.4276	$192.43	$192.45	$192.40
Purchase #3	$79.45	3.786%	$82.458	$82.46	$82.45	$82.50
Purchase #4	$134.90	3.563%	$139.7065	$139.71	$139.70	$139.70
Purchase #5	$105.65	13.621%	$120.0406	$120.04	$120.05	$120.00
Purchase #6	$102.99	10.540%	$113.8451	$113.85	$113.85	$113.80
Purchase #7	$39.66	6.211%	$42.1233	$42.12	$42.10	$42.10
7 purchase totals =	$820.04		$869.9539	$869.96	$869.95	$869.90