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	$166.56	7.524%	$179.092	$179.09	$179.10	$179.10
Purchase #2	$215.67	8.396%	$233.7777	$233.78	$233.80	$233.80
Purchase #3	$204.59	5.499%	$215.8404	$215.84	$215.85	$215.80
Purchase #4	$165.39	12.520%	$186.0968	$186.10	$186.10	$186.10
Purchase #5	$185.72	13.283%	$210.3892	$210.39	$210.40	$210.40
Purchase #6	$76.82	4.832%	$80.5319	$80.53	$80.55	$80.50
Purchase #7	$160.72	7.391%	$172.5988	$172.60	$172.60	$172.60
7 purchase totals =	$1,175.47		$1,278.3268	$1,278.33	$1,278.40	$1,278.30