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	$120.39	5.598%	$127.1294	$127.13	$127.15	$127.10
Purchase #2	$174.51	5.853%	$184.7241	$184.72	$184.70	$184.70
Purchase #3	$13.88	13.186%	$15.7102	$15.71	$15.70	$15.70
Purchase #4	$150.32	10.106%	$165.5113	$165.51	$165.50	$165.50
Purchase #5	$76.62	12.697%	$86.3484	$86.35	$86.35	$86.30
Purchase #6	$156.80	3.413%	$162.1516	$162.15	$162.15	$162.20
Purchase #7	$66.33	5.262%	$69.8203	$69.82	$69.80	$69.80
7 purchase totals =	$758.85		$811.3953	$811.39	$811.35	$811.30