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	$142.90	6.639%	$152.3871	$152.39	$152.40	$152.40
Purchase #2	$215.64	9.679%	$236.5118	$236.51	$236.50	$236.50
Purchase #3	$100.91	9.235%	$110.229	$110.23	$110.25	$110.20
Purchase #4	$60.65	3.788%	$62.9474	$62.95	$62.95	$62.90
Purchase #5	$92.51	7.125%	$99.1013	$99.10	$99.10	$99.10
Purchase #6	$136.63	4.357%	$142.583	$142.58	$142.60	$142.60
Purchase #7	$167.87	7.164%	$179.8962	$179.90	$179.90	$179.90
7 purchase totals =	$917.11		$983.6558	$983.66	$983.70	$983.60