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	$119.34	7.124%	$127.8418	$127.84	$127.85	$127.80
Purchase #2	$53.71	9.661%	$58.8989	$58.90	$58.90	$58.90
Purchase #3	$10.44	10.219%	$11.5069	$11.51	$11.50	$11.50
Purchase #4	$241.34	3.527%	$249.8521	$249.85	$249.85	$249.90
Purchase #5	$222.27	4.165%	$231.5275	$231.53	$231.55	$231.50
Purchase #6	$160.52	11.417%	$178.8466	$178.85	$178.85	$178.80
Purchase #7	$210.67	5.348%	$221.9366	$221.94	$221.95	$221.90
7 purchase totals =	$1,018.29		$1,080.4104	$1,080.42	$1,080.45	$1,080.30