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	$250.31	4.333%	$261.1559	$261.16	$261.15	$261.20
Purchase #2	$73.65	6.829%	$78.6796	$78.68	$78.70	$78.70
Purchase #3	$236.60	9.645%	$259.4201	$259.42	$259.40	$259.40
Purchase #4	$104.61	6.466%	$111.3741	$111.37	$111.35	$111.40
Purchase #5	$116.65	11.512%	$130.0787	$130.08	$130.10	$130.10
Purchase #6	$228.93	12.373%	$257.2555	$257.26	$257.25	$257.30
Purchase #7	$86.39	4.707%	$90.4564	$90.46	$90.45	$90.50
7 purchase totals =	$1,097.14		$1,188.4203	$1,188.43	$1,188.40	$1,188.60