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	$176.71	3.854%	$183.5204	$183.52	$183.50	$183.50
Purchase #2	$51.40	6.814%	$54.9024	$54.90	$54.90	$54.90
Purchase #3	$39.68	6.427%	$42.2302	$42.23	$42.25	$42.20
Purchase #4	$171.25	4.718%	$179.3296	$179.33	$179.35	$179.30
Purchase #5	$194.50	5.243%	$204.6976	$204.70	$204.70	$204.70
Purchase #6	$97.35	9.853%	$106.9419	$106.94	$106.95	$106.90
Purchase #7	$27.76	12.554%	$31.245	$31.25	$31.25	$31.20
7 purchase totals =	$758.65		$802.8671	$802.87	$802.90	$802.70