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	$25.99	5.658%	$27.4605	$27.46	$27.45	$27.50
Purchase #2	$241.95	3.650%	$250.7812	$250.78	$250.80	$250.80
Purchase #3	$152.94	12.573%	$172.1691	$172.17	$172.15	$172.20
Purchase #4	$154.90	3.539%	$160.3819	$160.38	$160.40	$160.40
Purchase #5	$250.61	13.153%	$283.5727	$283.57	$283.55	$283.60
Purchase #6	$131.47	8.396%	$142.5082	$142.51	$142.50	$142.50
Purchase #7	$184.41	3.678%	$191.1926	$191.19	$191.20	$191.20
7 purchase totals =	$1,142.27		$1,228.0662	$1,228.06	$1,228.05	$1,228.20