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	$29.81	7.702%	$32.106	$32.11	$32.10	$32.10
Purchase #2	$250.94	11.597%	$280.0415	$280.04	$280.05	$280.00
Purchase #3	$166.51	4.708%	$174.3493	$174.35	$174.35	$174.30
Purchase #4	$229.65	11.238%	$255.4581	$255.46	$255.45	$255.50
Purchase #5	$156.52	11.366%	$174.3101	$174.31	$174.30	$174.30
Purchase #6	$104.41	10.689%	$115.5704	$115.57	$115.55	$115.60
Purchase #7	$23.49	9.333%	$25.6823	$25.68	$25.70	$25.70
7 purchase totals =	$961.33		$1,057.5177	$1,057.52	$1,057.50	$1,057.50