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	$203.44	13.848%	$231.6124	$231.61	$231.60	$231.60
Purchase #2	$224.63	4.869%	$235.5672	$235.57	$235.55	$235.60
Purchase #3	$177.27	8.259%	$191.9107	$191.91	$191.90	$191.90
Purchase #4	$60.50	11.500%	$67.4575	$67.46	$67.45	$67.50
Purchase #5	$182.78	12.655%	$205.9108	$205.91	$205.90	$205.90
Purchase #6	$166.45	9.341%	$181.9981	$182.00	$182.00	$182.00
Purchase #7	$233.47	9.353%	$255.3064	$255.31	$255.30	$255.30
7 purchase totals =	$1,248.54		$1,369.7631	$1,369.77	$1,369.70	$1,369.80