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	$122.53	13.540%	$139.1206	$139.12	$139.10	$139.10
Purchase #2	$237.45	9.874%	$260.8958	$260.90	$260.90	$260.90
Purchase #3	$73.64	8.428%	$79.8464	$79.85	$79.85	$79.80
Purchase #4	$181.72	5.565%	$191.8327	$191.83	$191.85	$191.80
Purchase #5	$122.27	4.269%	$127.4897	$127.49	$127.50	$127.50
Purchase #6	$234.38	13.178%	$265.2666	$265.27	$265.25	$265.30
Purchase #7	$128.46	4.265%	$133.9388	$133.94	$133.95	$133.90
7 purchase totals =	$1,100.45		$1,198.3906	$1,198.40	$1,198.40	$1,198.30