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	$164.96	5.608%	$174.211	$174.21	$174.20	$174.20
Purchase #2	$185.59	7.443%	$199.4035	$199.40	$199.40	$199.40
Purchase #3	$19.50	3.362%	$20.1556	$20.16	$20.15	$20.20
Purchase #4	$206.28	9.352%	$225.5713	$225.57	$225.55	$225.60
Purchase #5	$28.43	10.689%	$31.4689	$31.47	$31.45	$31.50
Purchase #6	$74.97	4.162%	$78.0903	$78.09	$78.10	$78.10
Purchase #7	$193.96	8.545%	$210.5339	$210.53	$210.55	$210.50
7 purchase totals =	$873.69		$939.4345	$939.43	$939.40	$939.50