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	$54.35	5.872%	$57.5414	$57.54	$57.55	$57.50
Purchase #2	$123.73	8.471%	$134.2112	$134.21	$134.20	$134.20
Purchase #3	$130.63	11.494%	$145.6446	$145.64	$145.65	$145.60
Purchase #4	$21.78	13.145%	$24.643	$24.64	$24.65	$24.60
Purchase #5	$226.75	12.634%	$255.3976	$255.40	$255.40	$255.40
Purchase #6	$87.35	3.835%	$90.6999	$90.70	$90.70	$90.70
Purchase #7	$244.71	4.340%	$255.3304	$255.33	$255.35	$255.30
7 purchase totals =	$889.30		$963.4681	$963.46	$963.50	$963.30