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	$19.27	4.542%	$20.1452	$20.15	$20.15	$20.10
Purchase #2	$231.91	11.856%	$259.4052	$259.41	$259.40	$259.40
Purchase #3	$176.93	4.809%	$185.4386	$185.44	$185.45	$185.40
Purchase #4	$108.53	10.711%	$120.1546	$120.15	$120.15	$120.20
Purchase #5	$98.29	3.118%	$101.3547	$101.35	$101.35	$101.40
Purchase #6	$202.40	12.786%	$228.2789	$228.28	$228.30	$228.30
Purchase #7	$167.25	10.329%	$184.5253	$184.53	$184.55	$184.50
7 purchase totals =	$1,004.58		$1,099.3025	$1,099.31	$1,099.35	$1,099.30