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	$233.63	9.342%	$255.4557	$255.46	$255.45	$255.50
Purchase #2	$134.94	5.742%	$142.6883	$142.69	$142.70	$142.70
Purchase #3	$174.49	12.623%	$196.5159	$196.52	$196.50	$196.50
Purchase #4	$121.68	12.539%	$136.9375	$136.94	$136.95	$136.90
Purchase #5	$110.98	4.264%	$115.7122	$115.71	$115.70	$115.70
Purchase #6	$247.78	13.790%	$281.9489	$281.95	$281.95	$281.90
Purchase #7	$10.61	11.252%	$11.8038	$11.80	$11.80	$11.80
7 purchase totals =	$1,034.11		$1,141.0623	$1,141.07	$1,141.05	$1,141.00