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	$98.61	13.372%	$111.7961	$111.80	$111.80	$111.80
Purchase #2	$84.56	7.143%	$90.6001	$90.60	$90.60	$90.60
Purchase #3	$165.98	8.221%	$179.6252	$179.63	$179.65	$179.60
Purchase #4	$172.88	7.317%	$185.5296	$185.53	$185.55	$185.50
Purchase #5	$207.63	11.582%	$231.6777	$231.68	$231.70	$231.70
Purchase #6	$113.29	12.359%	$127.2915	$127.29	$127.30	$127.30
Purchase #7	$95.70	6.409%	$101.8334	$101.83	$101.85	$101.80
7 purchase totals =	$938.65		$1,028.3536	$1,028.36	$1,028.45	$1,028.30