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	$128.70	9.837%	$141.3602	$141.36	$141.35	$141.40
Purchase #2	$90.34	12.480%	$101.6144	$101.61	$101.60	$101.60
Purchase #3	$250.88	13.670%	$285.1753	$285.18	$285.20	$285.20
Purchase #4	$181.64	9.139%	$198.2401	$198.24	$198.25	$198.20
Purchase #5	$156.43	7.642%	$168.3844	$168.38	$168.40	$168.40
Purchase #6	$236.94	7.259%	$254.1395	$254.14	$254.15	$254.10
Purchase #7	$116.99	12.398%	$131.4944	$131.49	$131.50	$131.50
7 purchase totals =	$1,161.92		$1,280.4083	$1,280.40	$1,280.45	$1,280.40