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	$225.64	13.149%	$255.3094	$255.31	$255.30	$255.30
Purchase #2	$165.71	9.723%	$181.822	$181.82	$181.80	$181.80
Purchase #3	$139.51	6.716%	$148.8795	$148.88	$148.90	$148.90
Purchase #4	$24.46	12.175%	$27.438	$27.44	$27.45	$27.40
Purchase #5	$55.69	8.697%	$60.5334	$60.53	$60.55	$60.50
Purchase #6	$62.87	13.404%	$71.2971	$71.30	$71.30	$71.30
Purchase #7	$82.69	7.427%	$88.8314	$88.83	$88.85	$88.80
7 purchase totals =	$756.57		$834.1108	$834.11	$834.15	$834.00