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	$242.79	10.587%	$268.4942	$268.49	$268.50	$268.50
Purchase #2	$136.78	4.115%	$142.4085	$142.41	$142.40	$142.40
Purchase #3	$214.45	13.725%	$243.8833	$243.88	$243.90	$243.90
Purchase #4	$44.26	13.745%	$50.3435	$50.34	$50.35	$50.30
Purchase #5	$72.32	11.150%	$80.3837	$80.38	$80.40	$80.40
Purchase #6	$121.71	9.364%	$133.1069	$133.11	$133.10	$133.10
Purchase #7	$200.69	10.672%	$222.1076	$222.11	$222.10	$222.10
7 purchase totals =	$1,033.00		$1,140.7277	$1,140.72	$1,140.75	$1,140.70