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	$103.92	7.226%	$111.4293	$111.43	$111.45	$111.40
Purchase #2	$61.44	5.260%	$64.6717	$64.67	$64.65	$64.70
Purchase #3	$59.67	8.686%	$64.8529	$64.85	$64.85	$64.90
Purchase #4	$216.65	12.603%	$243.9544	$243.95	$243.95	$244.00
Purchase #5	$164.81	12.445%	$185.3206	$185.32	$185.30	$185.30
Purchase #6	$50.94	6.724%	$54.3652	$54.37	$54.35	$54.40
Purchase #7	$105.74	9.129%	$115.393	$115.39	$115.40	$115.40
7 purchase totals =	$763.17		$839.9871	$839.98	$839.95	$840.10