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	$55.39	8.352%	$60.0162	$60.02	$60.00	$60.00
Purchase #2	$90.42	11.272%	$100.6121	$100.61	$100.60	$100.60
Purchase #3	$245.30	13.445%	$278.2806	$278.28	$278.30	$278.30
Purchase #4	$179.54	9.550%	$196.6861	$196.69	$196.70	$196.70
Purchase #5	$36.40	9.103%	$39.7135	$39.71	$39.70	$39.70
Purchase #6	$71.65	9.379%	$78.3701	$78.37	$78.35	$78.40
Purchase #7	$229.47	11.295%	$255.3886	$255.39	$255.40	$255.40
7 purchase totals =	$908.17		$1,009.0672	$1,009.07	$1,009.05	$1,009.10