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	$237.48	3.416%	$245.5923	$245.59	$245.60	$245.60
Purchase #2	$234.70	10.107%	$258.4211	$258.42	$258.40	$258.40
Purchase #3	$169.27	9.589%	$185.5013	$185.50	$185.50	$185.50
Purchase #4	$246.77	3.712%	$255.9301	$255.93	$255.95	$255.90
Purchase #5	$123.55	12.854%	$139.4311	$139.43	$139.45	$139.40
Purchase #6	$99.78	3.374%	$103.1466	$103.15	$103.15	$103.10
Purchase #7	$127.45	6.564%	$135.8158	$135.82	$135.80	$135.80
7 purchase totals =	$1,239.00		$1,323.8383	$1,323.84	$1,323.85	$1,323.70