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	$137.79	13.627%	$156.5666	$156.57	$156.55	$156.60
Purchase #2	$211.75	8.336%	$229.4015	$229.40	$229.40	$229.40
Purchase #3	$120.57	11.449%	$134.3741	$134.37	$134.35	$134.40
Purchase #4	$152.37	3.698%	$158.0046	$158.00	$158.00	$158.00
Purchase #5	$35.72	9.256%	$39.0262	$39.03	$39.05	$39.00
Purchase #6	$71.95	9.449%	$78.7486	$78.75	$78.75	$78.70
Purchase #7	$102.33	8.682%	$111.2143	$111.21	$111.20	$111.20
7 purchase totals =	$832.48		$907.3359	$907.33	$907.30	$907.30