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	$138.25	3.192%	$142.6629	$142.66	$142.65	$142.70
Purchase #2	$131.88	6.867%	$140.9362	$140.94	$140.95	$140.90
Purchase #3	$130.45	9.501%	$142.8441	$142.84	$142.85	$142.80
Purchase #4	$70.78	6.804%	$75.5959	$75.60	$75.60	$75.60
Purchase #5	$59.83	3.795%	$62.1005	$62.10	$62.10	$62.10
Purchase #6	$149.51	12.830%	$168.6921	$168.69	$168.70	$168.70
Purchase #7	$30.38	4.453%	$31.7328	$31.73	$31.75	$31.70
7 purchase totals =	$711.08		$764.5645	$764.56	$764.60	$764.50