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	$49.81	11.802%	$55.6886	$55.69	$55.70	$55.70
Purchase #2	$37.65	7.166%	$40.348	$40.35	$40.35	$40.30
Purchase #3	$138.30	5.256%	$145.569	$145.57	$145.55	$145.60
Purchase #4	$42.87	8.499%	$46.5135	$46.51	$46.50	$46.50
Purchase #5	$210.87	3.597%	$218.455	$218.46	$218.45	$218.50
Purchase #6	$224.73	8.190%	$243.1354	$243.14	$243.15	$243.10
Purchase #7	$150.84	4.853%	$158.1603	$158.16	$158.15	$158.20
7 purchase totals =	$855.07		$907.8698	$907.88	$907.85	$907.90