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	$132.64	5.135%	$139.4511	$139.45	$139.45	$139.50
Purchase #2	$136.86	6.107%	$145.218	$145.22	$145.20	$145.20
Purchase #3	$218.76	8.208%	$236.7158	$236.72	$236.70	$236.70
Purchase #4	$138.41	12.336%	$155.4843	$155.48	$155.50	$155.50
Purchase #5	$47.27	13.408%	$53.608	$53.61	$53.60	$53.60
Purchase #6	$174.29	12.533%	$196.1338	$196.13	$196.15	$196.10
Purchase #7	$42.88	12.701%	$48.3262	$48.33	$48.35	$48.30
7 purchase totals =	$891.11		$974.9372	$974.94	$974.95	$974.90