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	$147.86	11.840%	$165.3666	$165.37	$165.35	$165.40
Purchase #2	$239.40	6.552%	$255.0855	$255.09	$255.10	$255.10
Purchase #3	$170.51	5.288%	$179.5266	$179.53	$179.55	$179.50
Purchase #4	$140.72	11.498%	$156.9	$156.90	$156.90	$156.90
Purchase #5	$165.81	6.353%	$176.3439	$176.34	$176.35	$176.30
Purchase #6	$42.27	10.823%	$46.8449	$46.84	$46.85	$46.80
Purchase #7	$107.46	8.546%	$116.6435	$116.64	$116.65	$116.60
7 purchase totals =	$1,014.03		$1,096.7110	$1,096.71	$1,096.75	$1,096.60